Annual report for the Norwegian National Seismic Network

Transcription

1 Annual report for the Norwegian National Seismic Network 2014 Supported by University of Bergen and Norwegian Oil and Gas Association Prepared by Department of Earth Science University of Bergen Allegaten 41, N-5007 Bergen April 2015

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3 CONTENTS 1 Introduction Data availability to the public Operation Operation NNSN The NORSAR Stations and Arrays Field stations and technical service NNSN NNSN achievements and plans NNSN achievements in NNSN plans for New developments at NORSAR Seismicity of Norway and surrounding areas for Velocity models and magnitude relations Events recorded by the NNSN The seismicity of Norway and adjacent areas Earthquakes in the southern North Sea Seismic activity at the Bárðarbunga system, Iceland Felt earthquakes Scientific studies The effect of higher noise levels on detection maps Development of a 3-D velocity model for Norway by I. Janutyte Using the Eskdalemuir array in Scotland for seismic monitoring of the North Sea region 38 6 Publications and presentations of NNSN data during Publications Reports Oral presentations Poster presentations References... 43

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5 1 Introduction This annual report for the Norwegian National Seismic Network (NNSN) covers operational aspects for the seismic stations contributing data, presents the seismic activity in the target areas and the associated scientific work carried out under the project. The report is prepared by the University of Bergen with contributions from NORSAR. The NNSN network is supported by the oil industry through the Norwegian Oil and Gas Association and the University of Bergen (UiB). 1.1 Data availability to the public All the data stored in the NNSN database are available to the public via Internet, or on manual request. The main web-portal for earthquake information is It is possible to search interactively for specific data, display the data locally (waveforms and hypocenters) and then download the data. Data are processed as soon as possible and updated lists of events recorded by Norwegian stations are available soon after recording. These pages are automatically updated with regular intervals. 2 Operation 2.1 Operation NNSN The University of Bergen (UiB) has the main responsibility to run the NNSN and operates 33 of the seismic stations that form the NNSN located as seen in Figure 1. NORSAR operates 3 seismic arrays, which also include broadband instruments, and three single seismometer stations (JETT, JMIC and AKN). In addition to the NNSN stations, waveform data from other selected stations in Finland (University of Helsinki), Denmark (GEUS), Sweden (University of Uppsala) and Great Britain (BGS) are transferred in real time and included in the NNSN database. In total data from 25 stations located in or operated by neighbouring countries are recorded continuously in Bergen and can be used for locating earthquakes, see Figure 1. Phase data from arrays in Russia (Apatity), Finland (Finess), Sweden (Hagfors) and stations operated by the British Geological Survey (BGS) are also included when available. The seismicity detected by the network is processed at UiB, however NORSAR also integrates their results in the joint database at UiB. In total, NORSAR provides data from 12 broadband stations to the NNSN. One station with real-time data is provided from the Ekofisk field by ConocoPhillips. The station HSPB is operated jointly between NORSAR and the Geophysical Institute, Polish Academy of Sciences, Warsaw, Poland and the stations BRBA and BRBB are a collaboration between NORSAR and the Kola Science Centre, Russian Academy of Sciences, Apatity, Russia. BRBA and BRBB are both located in Barentsburg, Svalbard. 1

6 Figure 1. Stations contributing to the Norwegian National Seismic network (NNSN). UiB operates 33 stations (red) and NORSAR operates the stations marked in blue, including the three arrays and stations AKN and JMIC. Seismic data recorded at stations located on Greenland and operated by GEUS are included in the NNSN real-time processing, Figure 2. These data are important for the location of earthquakes west of Jan Mayen and at the northern part of the Knipovich ridge to the Gakkel ridge. 2

7 Figure 2. Seismic stations in the arctic area. UiB is in the process of upgrading the NNSN by changing short period (SP) to broadband (BB) seismometers. A further effort is made to install additional high quality digitizers. The current status of this upgrade is shown in Table 1. As of today the numbers of SP, BB stations and stations with real time transmission are listed in Table 1. Table 1. Overview of UiB seismic stations Short Period Broadband Real time Number of stations (19 with natural period greater than 100 sec) The operational stability for each station is shown in 30 (not real time are 2 short period and 1 broadband stations on Jan Mayen) Table 2. The downtime is computed from the amount of data that are missing from the continuous recordings at UiB. The statistics will, therefore, also show when a single component is not working. This is done as the goal is to obtain as complete continuous data 3

8 from all stations as possible. Also, communication or computing problems at the centre will contribute to the overall downtime. In the case of communication problems, a station may not participate in the earthquake detection process, but the data can be used when it has been transferred. Thus, the statistics given allow us to evaluate the data availability when rerunning the earthquake detection not in real-time. The data completeness for the majority of the stations is above 95%, except for the following stations KMY, KTK1 and MOR8 (see technical service overview for details). Table 2. Data completeness in % for 2014 for all stations of the NNSN operated by UiB. Station Data completeness % Askøy (ASK) 96 Bergen (BER) 100 Bjørnøya (BJO) 100 Blåsjø (BLS) 98 Dombås (DOMB) 100 Fauske (FAUS) 100 (June-) Florø (FOO) 96 Hammerfest (HAMF) 100 Homborsund (HOMB) 95 Hopen (HOPEN) 100 Høyanger (HYA) 100 Jan Mayen (JMI) 100 Jan Mayen (JNE) 100 Jan Mayen (JNW) 100 Karmøy (KMY) 93 Kautokeino (KTK1) 76 Station Data completeness % Kings Bay (KBS) 98 Kongsberg (KONO) 98 Konsvik (KONS) 97 Lofoten (LOF) 100 Mo i Rana (MOR8) 88 Molde (MOL) 99 Namsos (NSS) 100 Odda (OOD1) 99 Oslo (OSL) 100 Skarslia (SKAR) 100 Snartemo (SNART) 98 Stavanger (STAV) 100 Steigen (STEI) 98 Stokkvågen (STOK) 98 Sulen (SUE) 95 Blussuvoll (TBLU) 97 Tromsø (TRO) 100 4

9 2.2 The NORSAR Stations and Arrays NORSAR is operating the following installations in Norway (with funding outside the NNSN): NOA (southern Norway, array, 42 sites, 7 3C broadband sensors and 35 vertical broadband sensors) ARCES (Finmark, array, 25 sites, 25 3C broadband seismic sensors 80 Hz) SPITS (Spitsbergen, array, 9 sites, 6 3C broadband sensors and 3 vertical broadband sensors) NORES (Hedmark, array, 9 3C short-period sensors, 9 infrasound sensors) JMIC (Jan Mayen, 3C broadband sensor ) AKN (Åknes, Møre og Romsdal, 3C broadband sensor) IS37 (Bardufoss, infrasound array, 10 sites) JETT (Jettan, Troms, 3C broadband sensor) In addition NORSAR receives and processes data in near realtime from: FINES (southern Finland, array, 16 sites, 2 3C broadband sensor, 1 3C short-period sensor and 15 short-period vertical sensors, operated by Institute of Seismology, Helsinki, Finland) HFS (Hagfors, Sweden, 10 sites, 1 3C broadband sensor and 9 short-period vertical sensors, operated by the Swedish Defence Reseearch Agency, Stockholm, Sweden) EKA (Eskdalemuir, United Kingdom, 20 sites, 1 3C broadband sensor and 20 shortperiod vertical sensors, operated by the United Kingdom National Data Centre, AWE Blacknest, UK) The location of these stations and arrays are presented in Figure 3. Figure 3. NORSAR seismic arrays/stations (NOA, NORES, ARCES, SPITS, JMIC, AKN) and contributing arrays/stations (HFS, FINES, EKA, BRBA, APA). 5

10 All NORSAR waveform data and parametric data are openly available and can be accessed through web-interfaces or direct means. The webpage provides access to general station information, to automatic and reviewed seismic bulletins, to real-time plots of short and long-period data, and to an AutoDRM request form for waveform data retrieval. The seismic array data are automatically processed and analysed. The fastest near realtime process Automatic Alert is based on single array detection and provides event locations within a few (1-3) minutes delay. The alerts with event and location details are published immediately on (which is also integrated into the NNSN website). A second automatic process called GBF (Generalized Beam Forming) awaits for automatic phase picks from all arrays and delivers more reliable/accurate results within up to a few hours delay. Automatically processed seismic events with magnitude larger than 2 (or 1.5 if the event is of special interest) are manually analysed and reviewed. In this step all available waveforms (also from single stations) are utilized. Graphical displays and parametric event data and for Automatic Alert, GBF and Reviewed bulletins can be found on Table 3 gives a summary of the phase detections and events declared by GBF and the analyst. Table 3. Phase detections and event summary. Jan. Feb. March April May June Phase detections Associated phases Un-associated phases Screened GBF events for Fennoscandia/Norway No. of events defined by the analyst July Aug. Sep. October Nov. Dec. Phase detections Associated phases Un-associated phases Screened GBF events for Fennoscandia/Norway No. of events defined by the analyst All data recorded at NORSAR are continuous. Table 3 provides a monthly overview on the data availability of 13 main data streams provided by NORSAR to NNSN. 6

11 Table 4. Systems recording performance (in % of data completeness) for 13 main data streams provided from NORSAR to NNSN. ARE0/ARA0 JMIC NAO01 NB201 NBO00 NC204 NC303 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec NC405 NC602 SPA0 AKN JETT HFC2 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Field stations and technical service NNSN The technical changes for each seismic station are listed below. It is noted if these changes are carried out by the respective local contact and not by the technical staff of UiB. When a station stops working, tests are made to locate the problem. Sometimes the reason cannot be found and the cause of the problem will be marked as unknown. Major changes during this reporting period of 2014 were: Ask (ASK) Bergen (BER) Bjørnøya (BJO1) : Visit. GPS antenna replaced due to timing problems : Digitizer malfunctioning due to lightning and was replaced All data between is lost. No visit or technical changes : Visit. Maintenance visit. An attempt was made to detect the cause of occasional noise on the vertical component and to plan for the upgrade in Blåsjø (BLS) : A UPS was malfunctioning and was removed by station contact. 7

12 Blussvoll (TBLU) Dombås (DOMB) Fauske (FAUS) Florø (FOO) Hammerfest (HAMF) Homborsund (HOMB) Hopen (HOPEN) Høyanger (HYA) Jan Mayen (JMI) JNE JNW Karmøy (KMY) No visit or technical changes. No visit or technical changes. New station : Vault constructed : Visit: Equipment installed : Visit: Station started : Visit: Station visited to center the seismometer. ICE router replaced with GSM : Visit: Water ingress checked and considered to be due to condensation. Vault lid to be replaced by concrete lid similar to the one used at SKAR. GSM router replaced with new unit : Visit by local operator. Condensation water was removed from the vault : Visit. Replace metal lid, frame and adapter ring with concrete lid. Removed water from the vault : Station down due to PC problems. PC replaced by local operator : The last half of December 2014 there was problems with unstable communication. Data lost for periods of this time. No visit or technical changes : A malfunctioning PC was replaced by the local contact. Data lost between : Visit. The existing STS-2 was replaced with a Trillium 120 PA sensor (the STS-2 was returned to NORSAR). This trip was also an opportunity to plan the station upgrade in No visit or technical changes : Inspection by local operator. Inspected by local operator. No technical changes. Inspected by local operator. No technical changes : Station down since Problems with the router. New router installed by local operator. Data lost. 8

13 : Station down since due to malfunctioning digitizer. New digitizer installed by local operator. Data lost. Kautokeino (KTK) Kings Bay (KBS) Kongsberg (KONO) Konsvik (KONS) Lofoten (LOF) Mo i Rana (MOR8) Molde (MOL) Namsos (NSS) Odda (ODD1) Oslo (OSL) Skarslia (SKAR) Snartemo (SNART) : Station down since Digitizer replaced by local operator and the station was restarted. Problem not solved : Station has been down since due to two broken digitizers. Digitizers replaced by local operator. All data has been lost : Digitizer broke down again, station awaiting visit : Visit. Inspection of the installation since the digitizer has been replaced several times. New recorder and power supply installed. Data lost between No visit or technical changes. No visit or technical changes : PC replaced by local operator. Station down since Data is lost. No visit or technical changes : PC replaced by local operator. Station down since Data is lost. No visit or technical changes. No visit or technical changes : Visit: GPS antenna replaced. Timing problem not solved : Cable to the GPS antenna was replaced by the local operator. The local operator had found that the cable had been damaged by a nesting bird : Visit. Upgrade of the station. Mounting a GPS antenna. Change the seismometer from Ranger SS-1 to Trillium 120PA. Change the digitizer from SARA to CMC-DM24S3-EAM : Visit. Inspection. No changes made : Visit. Inspection : Visit. Inspection. Removed condensation water from the vault : Station maintenance visit. Short period Ranger SS-1 seismometer installed. 9

14 Stavanger (STAV) Steigen (STEI) Stokkvågen (STOK) Sulen (SUE) Tromsø (TRO) No visit or technical changes. No visit or technical changes. No visit or technical changes. 08:04.14: Because of weak ICE signals, new GSM router installed : Data lost between due to power break. No visit or technical changes. 3 NNSN achievements and plans The overall purpose of the NNSN is to provide data both for scientific studies, but equally important for the routine observation of earthquakes. This in principle means that broadband seismometers are desired at all sites. However, in areas where additional stations are deployed for local monitoring, short-period seismometers are sufficient. The number of broadband seismometers in the network will be increased to replace existing short period instruments. A general goal for the future development has to be to achieve better standardization in particular with the seismometers and digitizers. The total number of stations for now should remain stable, but it is important to improve the overall network performance. 3.1 NNSN achievements in 2014 Upgrade: Station OSL was upgraded with a Trillium sensor and Guralp digitizer. The new station close to Fauske (FAUS), was installed during June The first data recorded June 23 rd. The station has been performing well and has very low noise levels. At Hopen the STS2 seismometer has been replaced with a Trillium 120 instrument, and construction of new vault was started. The STS2 will be returned back to NORSAR. Data from the new NEONOR2 project with temporary deployments in Nordland are available to the NSNN. 17 of the 25 stations are operational with communication and data are transferred to Bergen and processed as part of the daily routines. Staff from UiB and NORSAR visited University of Helsinki 29. September to 3. October to discuss the issue of identification of explosions. The number of stations for real-time detection has been increased by including more stations from Greenland and the UK. 3.2 NNSN plans for

15 Hopen: The station is to be improved, a new vault has been started by digging and the new vault will be installed in Bjørnøya: A new vault installation will be made in Construct a new station on Varanger peninsula. Site selection has started and a site at Vestre Jakobselv has been chosen. Initiate the plans for finding new site for station TBLU (Trondheim). The local authority in Stjørdal, north of Trondheim, has been contacted to find a possible site for noise measurements. The research and development activity will continue in close collaboration between UiB and NORSAR. Strengthen the collaboration with NORSAR on data processing through technical visits. Collaborate with other Scandinavian countries. The felt earthquake in Sweden in September 2014 demonstrates the need for collaboration between the Scandinavian countries about macroseismic studies. Also it is of interest to receive continuous data from more stations located in Sweden. Exchange of data between the Icelandic Meteorological Office and UiB would increase the location accuracy in the NNSN database for large earthquakes located in the vicinity of Iceland and in the area between Iceland and Jan Mayen. As of today data is available on request. 3.3 New developments at NORSAR The ARCES array had a major upgrade in September Sensors and digitizers were updated at each of the 25 sites and installed a new central acquisition system. In order to minimize data loss and to keep continuity the replacement was made during a time window of 3 days having old and new systems operational in parallel. All 25 sites have now threecomponent broadband sensors with hybrid response function, and sampling is at 80 Hz. The hybrid response function allows us to be very sensitive in the medium-high frequency range (essential for the test ban treaty monitoring), but also not to clip in the case of large far regional and global earthquakes. Figure 4. Old (dashed) and new (solid lines) instrument response fuctions at the ARCES array 11

16 In November 2014 a new station JETT at Jettan, Troms, was installed. The main purpose of the station is to monitor local seismicity associated with the unstable rock slope of the Nordnesfjellet. The instrument is a 3C Guralp ESPC with a bandwidth from 60s 100Hz. Sampling is at 200 and 40 Hz. The station is permanent and has been fully integrated into the NORSAR network. Figure 5. New site JETT at Nordnes, Troms 4 Seismicity of Norway and surrounding areas for 2014 The earthquake locations presented have been compiled from all available seismic stations as described above. All phase data are collected by UiB, and a monthly bulletin is prepared and distributed. All local and regional earthquakes recorded on NNSN stations are presented on the web pages and the largest are also ed to the European-Mediterranean Seismological Centre (EMSC) to be published on the EMSC web pages. A brief overview of the events published in the monthly bulletins is given in this annual report. Macroseismic data for the largest felt earthquakes in Norway are collected, and macroseismic maps are presented. Local, regional and teleseismic events that are detected by the UiB network are included. The merging of data between NORSAR and UiB is based on the following principles: i) All local and regional events recorded by NORSAR that are also detected by the NNSN network are included. ii) All local and regional events with local magnitude larger than 1.5 detected by NORSAR and not recorded by the NNSN are included. iii) All teleseismic events recorded by NORSAR and also detected by the NNSN are included. iv) All teleseismic events with NORSAR magnitude M b 5.0 are included even not detected by the NNSN. Data from the British Geological Survey (BGS) and the Geological Survey of Denmark and Greenland (GEUS) are included in the database in Bergen following similar criteria as 12

17 mentioned above, however only events located in the prime area of interest, N and 15 W-35 E, and with magnitude 2.0 are included. Identified earthquakes located in northern Scandinavia, are routinely ed from University of Helsinki and included in the NNSN database following the principles above. Since 16 august 2014, there has been a series of earthquakes (swarms) related to the Bárðarbunga system at Island. Earthquakes with M> has also been registered at NNSN stations. For these earthquakes locations and magnitude from the Island Meteorological Office (IMO) has been included in the NNSN database. 4.1 Velocity models and magnitude relations The velocity model used for locating all local and regional events, except for the local Jan Mayen events, is shown in Table 4 (Havskov and Bungum, 1987). Event locations are performed using the HYPOCENTER program (Lienert and Havskov, 1995) and all processing is performed using the SEISAN data analysis software (Havskov and Ottemöller, 1999). Table 4. Velocity model used for locating all local and regional events, except for the local Jan Mayen events (Havskov and Bungum, 1987). P-wave velocity Depth to layer (km/sec) interface (km) Magnitudes are calculated from coda duration, amplitudes or displacement source spectra. The coda magnitude relation was revised in 2006 (Havskov & Sørensen 2006). The coda wave magnitude scale (M C ) is estimated through the relation M C = log10(t) D where T is the coda length in seconds and D is the epicentral distance in km. The new scale made M C more consistent with M L since M C in general is reduced. For this report all data are updated using the new magnitude scale. When instrument corrected ground amplitudes A (nm) are available, local magnitude M L is calculated using the equation given by Alsaker et al. (1991): M L = 1.0 log(a) log(d) D where D is the hypocentral distance in km. 13

18 The moment magnitude M w is calculated from the seismic moment M 0 using the relation (Kanamori, 1977) M w = 0.67 log(m 0 ) 6.06 The unit of M 0 is Nm. The seismic moment is calculated from standard spectral analysis assuming the Brune model (Brune, 1970) and using the following parameters: Density: 3.0 g/cm 2 Q = 440 f 0.7 P-velocity = 6.2 km/s S velocity = 3.6 km/s For more computational details, see Havskov and Ottemöller, (2003). For the Jan Mayen area, a local velocity model (see Table 5) and coda magnitude scale is used (Andersen, 1987). Table 5. Velocity model used for locating local Jan Mayen events. P-wave velocity Depth to layer (km/sec) interface (km) The coda magnitude scale for Jan Mayen which is used in this report is given by Havskov & Sørensen (2006). This scale was implemented in 2006 but all events used in this report are updated during April/May M C = 3.27 log(t) D where T is the coda duration and D is the epicentral distance in km. The regional and teleseismic events recorded by the network are located using the global velocity model IASPEI91 (Kennett and Engdahl, 1991). Body wave magnitude is calculated using the equation by Veith and Clawson (1972): Mb = log(a/t) + Q(D,h) Here h is the hypocentre depth (km), A is the amplitude (microns), T is period in seconds and Q(D,h) is a correction for distance and depth. Surface wave magnitude Ms is calculated using the equation (Karnik et al., 1962): Ms = log(a/t) log(d)

19 where A is the amplitude (microns), T is period in seconds and D is the hypocentral distance in degrees. Starting from January 2001, the European Macroseismic Scale, EMS98, (Grünthal, 1998) has been used. All macroseismic intensities mentioned in the text will refer to the EMS98 instead of the previously used Modified Mercalli Intensity scale. The two scales are very similar at the lower end of the scale for intensities less than VII. 4.2 Events recorded by the NNSN Based on the criteria mentioned in section 4, a total of 5,892 local and regional events, were detected by the NNSN during Of these local and regional events, 50% were large enough to be recorded by several stations and hence could be located reliably, and are not classified as probable explosions. The numbers of local/regional and teleseismic events, recorded per month in 2014 are shown in Figure 6. The average number of local and regional events recorded per month is 491. A total of 1025 teleseismic events were recorded in 2014 and the monthly average of teleseismic earthquakes in the NNSN database, is 86. In addition to the locations determined at UiB and NORSAR, also preliminary locations published by the USGS (United States Geological Survey) or the EMSC (European Mediterranean Seismological Centre) based on the worldwide network are included for earthquakes also registered by NNSN stations JAN MAR MAY JUL SEP NOV Figure 6. Monthly distribution of local/regional and distant events, recorded during UiB, as an observatory in the global network of seismological observatories, reports phases from the teleseismic recordings. All events (teleseismic, regional and local) recorded from January to December 2014 with M 3 are plotted in Figure 7. 15

20 Figure 7. Epicentre distribution of earthquakes with M 3.0, located by the NNSN from January to December Teleseismic events recorded only by NORSAR have M 5.0. Monthly station recording statistics from January to December 2014 are given in Table 6 and 7. This table shows, for each station, local events recorded on more than one station and recorded teleseismic events. The statistics are based on the analysed data and are taken from the database. Table 6 and 7 show both earthquakes and explosions, and that the large number of detections at KTK mainly is due to explosions at the Kirruna/Malmberget mines in Sweden. The MOR station also records the Kirruna/Malmberget explosions, but in addition the station records a large number of explosions at the Rana Grube and local earthquakes. These earthquakes are also recorded on the stations FAUS, STOK and KONS and, therefore, the number of recorded earthquakes in this region is higher. The following was observed from Table 6 and 7: The station at Fauske (FAUS) was in operation from June 2014 and the first event was recorded June 23 rd. As SKAR, this station has a high S/N ratio and records a high number of events. The number of local earthquakes recorded in the arctic area increased in the time between April to August as can be seen on KBS and HOPEN TBLU and OSL are recording mostly teleseismic earthquakes, which is as expected due to their location in noisy environment. Stronger local earthquakes will however be detected. The stations KONS, STOK and MOR8 continue to record a relatively large number of small earthquakes and explosions in the area. Temporary stations were deployed during fall 2013 and an increase in smaller events recorded and located in this area is expected during the NEONOR2 project period. 16

21 Table 6. Monthly statistics of events recorded at each station for January-June Abbreviations are: L = Number of local events recorded at more than one station and D = Number of teleseismic events recorded at the station. JANUARY FEBRUARY MARCH APRIL MAY JUNE STATION L D L D L D L D L D L D ASK BER BJO BLS DOMB FAUS FOO HAMF HOMB HOPEN HYA JMI JMIC JNE JNW KBS KMY KONO KONS KTK LOF MOL MOR NSS ODD OSL SKAR SNART STAV STEI STOK SUE TBLU TRO NORSAR ARCES SPITS

22 Table 7. Monthly statistics of events recorded at each station for July-December Abbreviations are: L = Number of local events recorded at more than one station and D = Number of teleseismic events recorded at the station. JULY AUGUST SEPT OCT NOV DEC STATION L D L D L D L D L D L D ASK BER BJO BLS DOMB FAUS FOO HAMF HOMB HOPEN HYA JMI JMIC JNE JNW KBS KMY KONO KONS KTK LOF MOL MOR NSS ODD OSL SKAR SNART STAV STEI STOK SUE TBLU TRO NORSAR ARCES SPITS The seismicity of Norway and adjacent areas The main area of interest is defined as 54-82N and 15W-35E. We also show the seismicity for the Arctic region including the Barents Sea defined by coordinates N and 20 W-50 E. A total of 3522 of the recorded events are located inside the NNSN prime area, 54 N-82 N and 15 W-35 E. During analysis and using the explosion filter (Ottemöller, 1995), 34% of these events were identified as probable explosions. After including stations from the NORSAR array the number of located small events has increased in eastern Norway. Figure 8 shows all local/regional events in the prime area, analysed and located during Among these, 385 are located in the vicinity of Jan Mayen. Figure 9 shows the location of every earthquake (known and probable explosions removed) located within the prime area with one of the calculated magnitudes above 3. Table 8 lists the same earthquakes with all earthquakes located close to the Mid-Atlantic ridge removed. 18

23 Figure 8. Epicentre distribution of events analysed and located in Earthquakes are plotted in red and probable and known explosions in blue. For station locations, see Figure 1. It should be emphasized that the magnitude calculation for the earthquakes located on the oceanic ridge in the Norwegian Sea uses the same formula as for mainland Norway. As the scale is not appropriate for this region, the magnitudes for these earthquakes are underestimated. Most of the recorded earthquakes in this area have magnitudes above 3.0 if they are recorded on Norwegian mainland stations. 19

24 Figure 9. Epicentre distribution of located events with one of the calculated magnitudes above or equal to 3.0. For station location, see Figure 1. The largest local or regional earthquake in 2014, recorded on Norwegian stations and within the prime area, occurred on September 15 th at 13:08(UTC) in Vestmanland, Sweden. The earthquake had a magnitude of M W =4.1. Along the mid-atlantic ridge a large number of earthquakes occur with magnitude above 3 which is approximately the detection level along the Mohns ridge. Of the 22 located earthquakes with magnitude above 4, 20 were located along the ridge mostly along the Mohns ridge. The magnitudes calculated for earthquakes in the Norwegian-Greenland sea are expected to be underestimated. 20

25 Table 8. Earthquakes located in the vicinity of mainland Norway and in the Svalbard area (blue background) with any magnitude above or equal to 3.0 for the time period January through December In cases where all BER magnitudes are below 3 but the event still is included in the list, NORSAR (NAO) or the British Geological Survey (BGS) has reported a magnitude of 3.0 or larger. Abbreviations are: HR = hour (UTC), MM = minutes, Sec = seconds, L = distance identification (L=local, R=regional, D=teleseismic), Latitud = latitude, Longitud = longitude, Depth = focal depth (km), F = fixed depth, AGA = agency (BER=Bergen), NST = number of stations, RMS = root mean square of the travel-time residuals, Ml = local magnitude and Mw = moment magnitude. Year Date HRMM Sec L Latitud Longitud Depth F AGA NST RMS Ml Mw L F BER L F BER L F BER L F BER L F BER L F BER L F BER L F BER L F BER L F BER L F BER L F BER The most significant earthquakes in the vicinity of the Norwegian mainland were: September 15 th 2014, 13:07(UTC) located in Sweden with a magnitude of M W =4.1. This earthquake was widely felt in southern Sweden (Figure 19) and in Sør-Trøndelag and Hedmark, Norway (Rissa, Tromdheim, Melhus, Røros and others) Offshore, an earthquake occurred September 30 th in the central North Sea. The earthquake was located at N 1.76 E with magnitudes ML BER =2.7 and ML BGS =3.1. The earthquake was registered both on Norwegian and British seismic stations Seismicity in Nordland Figure 10 shows the seismicity in Nordland since The area includes the locations of earthquake swarm activity such as Meløy, Steigen and Stokkvågen. The latter two areas are clearly visible on the map. Steigen was active between 2007 and 2008, but has been relatively quiet since then. The activity in the Stokkvågen area has been nearly continuous, and specific clusters in time and space have occurred. 21

26 Figure 10. Seismicity in the Nordland area. Red circles show seismicity for , and blue circles show seismicity for Known and probably explosions are excluded. The Petromaks funded project NEONOR2 started in 2013 and is a collaboration between NGU, Kartverket, the University of Bergen (UiB), NORSAR and NPD. The prime objectives of NEONOR2 are: to promote the understanding of regional-scale stress and strain dynamics in the Nordland area which has proved to be the tectonically most active area in Norway. The secondary objectives are to Obtain a new seismicity map of the Nordland region, relevant for geohazard evaluation Explore combined inversion methods to determine the regional stress field by integrating GPS, DInSAR, seismic data, in situ stress, and mapped faults Quantify the contribution of Pleistocene sediment redistribution on the present-day stress field using numerical modelling 22

27 Estimate the Pleistocene palaeo-stresses and palaeo-temperatures using numerical modelling Figure 11. Map of stations deployed in Northern Norway in 2013/2014. As a part of the NEONOR2 project temporary seismic stations were deployed. During the months from August to November 2013, 15 seismic stations were installed by UiB, and 5 stations by NORSAR. Six more stations were installed by NORSAR in The locations of the NEONOR2 stations are shown in Figure 11. Data from many of the stations are continuously transferred to Bergen and are used in the daily processing. 23

28 4.3.2 Seismicity in the arctic area With the mainland stations on the Lofoten, in Tromsø and Hammerfest, the network on Jan Mayen, and stations on Bjørnøya, Hopen and Svalbard, the network detection capability in the arctic area is relatively good. We define the arctic area as the region N and 20 W-50 E. Most of the activity falls into three areas: Jan Mayen, the Mid-Atlantic ridge and Storfjorden southeast of Svalbard, as can be seen in Figure 12. During 2014 also data from Danish stations on Greenland were used and this has increased the location accuracy for earthquakes west of Jan Mayen and northwest of Svalbard. The number of earthquakes recorded on enough stations to be located, have increased. Figure 12. Seismicity in the Norwegian arctic area during A total of 2116 located earthquakes Seismicity in the Jan Mayen area Jan Mayen is located in an active tectonic area with two major structures, the Mid Atlantic ridge and the Jan Mayen fracture zone, interacting in the vicinity of the island. Due to both tectonic and magmatic activity in the area, the number of recorded earthquakes is higher than in other areas covered by Norwegian seismic stations. During 2014 a total of 200 earthquakes were located as seen in Figure 13 and of these, six had a magnitude equal or above

29 The largest earthquake in the Jan Mayen region in 2014 occurred on 04 th March at 02:59 (UTC) and the magnitude is estimated to 4.8. The earthquake is located slightly north of the island in the Jan Mayen fracture zone. Figure 13. Earthquakes located in the vicinity of Jan Mayen during The number of recorded earthquakes in the Jan Mayen area has varied over the last years (Figure 14). The number of relatively strong earthquakes (M 3) shows smaller time variation than for the smaller earthquakes. The increases in 2004 and 2005 were due to the M=6.0 earthquake in 2004 and its aftershocks (Sørensen et al., 2007). The same is true for 2011, where the M=6.0 earthquake on 29 January was followed by a sequence of aftershocks. The 30 August 2012 earthquake with its fore and aftershocks clearly increases the number of recorded events in 2012 compared with previous years, making it the largest number of recorded events since For 2014 the number of earthquakes has increased slightly, with fourteen earthquakes with magnitude 3 or above. 25

30 Total number of recorded earthquakes Number of earthquakes with magnitude larger or equal to 3 Figure 14. Yearly distribution of earthquakes located in the Jan Mayen area since The area is as shown in Figure Seismicity in Storfjorden, Svalbard The Storfjorden area southeast of Svalbard, defined by latitude N and longitude 16-22E, has been seismically active since the M w =6.0 earthquake on 21 February A preliminary study was presented by Piril et al. (2008). One of the main objectives from this study was to resolve the source mechanism, which was found to be oblique-normal. This result was found from the inversion of both regional and teleseismic data. The earthquake had a high number of aftershocks. A total of more than 20 earthquakes with magnitude larger than M=4 have occurred in the area since An interesting question is whether the earthquakes now are aftershocks to the event in From the monthly number of all detected earthquakes, shown in Figure 15, it seems that the activity had decreased until the start of 2009 and then remained relatively low until late In 2010 the number had increased again and remained mostly stable in This is mostly explained by an increase in the number of smaller earthquakes as seen by the almost constant levels of earthquakes with M>2.5 since The better detection was due to usage of the data from the Hornsund (HSPB) station. In 2012 (270 earthquakes) and 2013 (206 earthquakes), it appears as if the overall activity is decreasing slightly, although still continuing. The total number of events located in the Storfjorden area in 2014 was around 314, an increase compared to the previous years. 26

31 Figure 15. Monthly number of earthquakes in the Storfjorden area since January The colours show: grey all events, red M>2.5, blue M>4.0. Figure 16 shows both a map with the seismicity since 2000 and the distribution of events over time. The onset of the activity in the Storfjorden area in February 2008 is obvious from the time plot. The seismicity since 2011 is mostly concentrated in the southwestern half of the area that has been active since The six largest earthquakes all occurred in the western part of Storfjorden, the largest (M=4.1) can be seen north of the cluster seen on Figure

32 Figure 16. Seismicty in the Svalbard area. Bottom: Earthquakes occurring in 2014 are plotted in yellow circles. Red circles show seismicity for The blue triangles give the station locations. Top: Seismicity in the same area is plotted as latitude as function of time. 28

33 4.4 Earthquakes in the southern North Sea During 2014 one earthquake were detected and located in the southern North Sea as shown in Figure 17. The earthquake occurred on September 30, 2014 at 10:59 with a local magnitude 2.7 (BER), 3.1 (BGS) and 2.7 (NAO) and is located to N, 1.66 E. Figure 17. The earthquake located in the southern North Sea during Seismic activity at the Bárðarbunga system, Iceland On 16 August 2014 an earthquake swarm occurred at the Bárðarbunga volcano, Iceland. The earthquakes were located to the eastern part of the system. During the first few days only, several thousand earthquakes were recorded. The NNSN network recorded most of the largest, M> 4.5, earthquakes located to the Bárðarbunga system. Between 23 rd August and 31 st December 2014, 51 earthquakes were located using the NNSN stations, most with magnitudes above 5.0. Locations from the Icelandic Met Office were added to the NNSN database for earthquakes recorded at NNSN stations. 4.6 Felt earthquakes In total, 17 earthquakes were reported felt and located within the target area during 2014 (see Table 9 and Figure 18). Not all earthquakes were felt in Norway. For the Jan Mayen Island the number of felt earthquakes is expected to be larger than reported. 29

34 Figure 18. Location of the 17 earthquakes reported felt during Eight of the earthquakes are felt in Norway. From 2006 it is possible to report felt earthquakes over the internet. When an earthquake is reported felt to UiB shortly after the origin time, questionnaires are available for the public on the site This may result in a higher number of questionnaires returned and therefore a need for new routines when processing the data. But for felt earthquakes the public has to be made aware of the questionaries which is done by informing when UiB is contacted by media or private persons. For the widely felt earthquake in Sweden no questionaries were received in Bergen and estimates of the intencities can only be made using information found in newspapers or by contacting locals directly. 30

35 Table 9. Earthquakes reported felt in the BER database in Abbreviations are: M L = local magnitude and M w = moment magnitude, W: questionnaires received on web (Y/N). Earthquakes reported felt in Norway are marked in colour. Nr Date Time (UTC) Max. Intensity (MMI) Magnitude (BER) Instrumental epicentre location :59 M L =2.3, M L =2.8(NAO) 69.89N / 25.31E N :39 M L =2.8(BGS),M L = N / 4.56E Y :36 M L =2.7, M L =2.6(HEL) 66.94N / 13.43E Y :16 M L =2.2, M L =2.5(NAO) 67.16N / 20.78E M L =2.5, M L =2.4(NAO) 62.36N / 6.04E N :03 M L = N / 15.24E N :36 M L =2.9, M L =2.9(BGS), 56.84N / 5.16W :54 M L =3.9, M L =4.3(BGS) 49.09N / 2.37W :36 M L = N / 14.91E :08 M L =4.2,Mb=4.8, 61.66N / 14.27E N M L =4.7(NAO) :49 M L =1.9, M L =2.4(NAO) 60.57N / 11.77E N :23 M L =2.1, 55.80N / 3.20W :23 M L =2.6, M L =2.6(BGS) 55.10N / 3.65W :18 M L = N / 27.41E M L =2.0, M L =2.0(BGS) 55.81N / 3.20W :57 M L =1.8, M L =2.2(NAO) 66.18N / 12.99E N :21 M L =1.9, M L =2.0(BGS) 54.51N / 3.05W W The largest felt earthquake during 2014 was the earthquake occurring in Sweden 15 th September at 13:08. The earthquake was reported felt from Trøndelag and Hedmark. UiB was contacted by the newspaper Adressa which had received several phone calls and messages on Facebook from Trondheim, Inderøy, Melhus, Orkanger, Røros and south along the Norwegian/Swedish border, Østlendingen reported that the earthquake was felt in Trysil, Elverum and Skarnes in southern Hedmark. Questionnaires were published on web, but no answers were received from the Norwegian side of the border. The University of Uppsala received reports and a map with reported intensities is presented in Figure 19. Judging by the statements from the people interviewed in the local newspapaer the earthquake were felt at intensity IV in the Trondheim area and possible III-IV in Hedmark. 31

36 Figure 19. Intensities for the earthquake 15 th September at 13:08. Data from Sweden (circles) are provided by Bjørn Lund, University of Uppsala. White triangles are locations where the earthquake is felt, but at present with unknown intensity. 32

37 5 Scientific studies This section will present an overview of research work that is carried out under the NNSN project. The main objective of this work is to improve the understanding of earthquakes and the seismological models in the region, mostly by using data recorded by the NNSN. Results will be used to improve the NNSN monitoring service. 5.1 The effect of higher noise levels on detection maps by A. Demuth and L. Ottemöller The ambient seismic noise levels for the NNSN were calculated to 1) evaluate station performance, 2) develop noise models for Norway, 3) investigate temporal and geographical differences, 4) quantify the link between weather data and noise levels, and 5) model the effect of cultural noise on the detection levels. The performance of a seismic station at long periods (T>30 sec) results from the vault construction and the instrumentation that is used. For the NNSN, most very-broadband sensors are of the same type and differences between stations mostly reflect vault construction practice. The recently constructed stations FAUS and SKAR perform well, while some others that were originally constructed for short period stations show poor performance. For high frequencies (f>4hz) the expected difference between day and night can be seen clearly, especially for the stations located within cities, such as BER, OSL and TBLU. The noise levels between 4 and 16 sec are mostly related to ocean waves, and there is a clear correlation between seismic noise and weather conditions for Norway. From spectrograms that show the change of noise levels over time it is possible to make the link to storm systems that move across the North Atlantic. We showed in particular that local wave height maxima are a good approximation for the noise level wave height relation and that wave height variations closer to the stations have a stronger influence on the noise level. We quantified the relation between wave height and noise levels. For example, a wave height change of around 4m at km distance to a coastal station decreases the detectability of a local magnitude by 0.5 units. While stations closer to the shore and hence the source of the oceanic noise show higher levels of noise, there is otherwise no clear geographical pattern of noise level variation for Norway. Using the mode noise levels of most very broadband stations in Norway observed during the summer, we constructed a low noise model (Figure 20), which shows similar noise levels as the global model derived by Peterson (1993). However, it is seen that in the summer the microseismic peak is shifted toward shorter periods around 3 sec. 33

38 Figure 20. Computed noise mode levels for stations of the NNSN (blues) and the low noise model for Norway (red). Figure 21. Observed smallest magnitude as given in the NNSN catalogue within each grid cells. 34

39 Figure 22. Calculated detection maps, station locations are given by black triangles. Left: Assuming same noise levels at all stations; and Right: Assuming higher noise levels at stations given by white triangles. We computed detection maps for the NNSN (Figure 22). This is done by requiring four stations to detect an event and computing the distance between each grid point and the fourth furthest station from that point. Based on an estimate of the smallest magnitude that can be observed at that distance, the detection level is assigned to that grid point. While this is a rather simple approach we can test that it provides useful results by comparing with the observed smallest magnitudes (Figure 21). Figure 22 (left) shows the detection levels assuming the same noise levels at all stations. However, using the results from the noise analysis and translating higher noise at frequencies above 3 Hz to increased detection it is possible to consider obvious differences in individual station detectability. Figure 22 (right) shows the result when considering the higher cultural noise in Bergen, Oslo, Trondheim, Stavanger and Tromsø. As expected the detection levels around the stations goes up. Comparing to (Figure 21) we see that offshore south-western Norway and in Central Norway around Trondheim not as small earthquakes as in other similar areas are detected. While this may have natural causes, it also matches the corresponding pattern of reduced detectability. Overall, this allows to better understand catalogue completeness and to identify where the network requires improvement. 35

40 5.2 Development of a 3-D velocity model for Norway by I. Janutyte The aim is to develop a new 3-D crustal velocity model for Norway. As Norway is elongated geographically, its territory is divided into different parts and studies are performed separately. During the given period we focused on the southern and northern (Nordland area) on-shore parts of Norway. The development of the 3-D velocity model has two steps: 1) finding optimal 1-D velocity model with VELEST program (Kissling et al., 1994) which is implemented into the SEISAN program package, 2) obtaining 3-D velocity model with FMTOMO program (Rawlinson and Sambridge, 2005) while using the optimal 1-D velocity model obtained in step 1. The southern study area is N and 2-14 E, and the dataset contains 175 seismic events of different types analyzed both at NORSAR and UiB. The northern study area is N and 7-19 E, and the dataset contains over 560 seismic events recorded by stations of both the NNSN and the NEONOR2 projects, and analyzed at UiB. The velocity models for both study areas extend from the surface down to 80 km depth. In order to obtain the optimal parameters and 1-D velocity models for both territories we tested different velocity models. After analysis of the VELEST results we defined the optimal 1-D velocity models for both southern and northern parts of Norway. These models could be used to locate the local seismic events with higher precision in daily analysis. In our study these models were used as the reference velocity models for the inversions with the FMTOMO program. Before implementing the optimal 1-D velocity models into the FMTOMO program, they were transformed into the velocity models with two layers and the gradient velocity changes in each layer (Figure 23). The studies of the P-wave velocities have been performed so far. The resolution of the results obtained with FMTOMO program has been tested performing the synthetic tests like checkerboards (Figure 24), spike and artificial geological structures, and calculating the hit matrices (Figure 25). The resolution tests revealed that the best resolved parts are in the middle of the study areas, which is not surprising, because in here is the best ray coverage and, most important, most of the ray-crossing. The hit matrix revealed that the maximum depth of the results in the southern part is down to 45 km, while about 35 km in the northern part of Norway. The inversion results obtained with the real datasets (Figure 26) reveal complex velocity structure in the southern part of Norway and highly varying Moho boundary in Nordland. 36

41 Figure 23. Reference P wave velocity models for southern (brown line) and northern (blue line) Norway used in FMTOMO program. Figure 24. Checkerboard velocity models for southern (left) and northern (right) Norway. Shown depth slices at 10 km depth, and vertical slices along the depicted latitudes (N) and longitudes (E). The blocks in both models vary ±0.6 km/s compared to the reference velocity model. Figure 25. Hit matrices calculated for southern (left) and northern (right) Norway. Shown are depth slices at 10 km depth, and vertical slices along the depicted latitudes (N) and longitudes (E). The hits calculated for the given cells and normalized according to the total amount of rays used in the separate inversions. 37

42 Figure 26. Inversion results obtained with the real datasets for southern (left) and northern (right) Norway. Depth slices are shown at different indicated depths (km), and vertical slices are shown along the depicted latitudes (N) and longitudes (E). Different colors indicate smaller (red) or larger (blue) P wave velocity values compared to the reference velocity model presented in Fig. 1. Dashed lines on horizontal slices show intersection (Moho boundary) between the two layers at the given depths, while at vertical slices the Moho boundary is depicted as a solid line. 5.3 Using the Eskdalemuir array in Scotland for seismic monitoring of the North Sea region by F. Ringdal, T. Kværna and J. Schweitzer Continuous data from three single three-component stations in Scotland and England are currently being used in the operations of the Norwegian National Seismic Network. These stations, including the GSN station ESK (Eskdalemuir) are particularly important for monitoring the earthquake activity in the North Sea area. A 20-element seismic array (EKA) is also located close to Eskdalemuir (see Figure 27), and the aim of this study has been to evaluate the effect of including data from the EKA array in the seismic monitoring of the North Sea region. Figure 27. Geometry of the Eskdalemuir seismic array (EKA) in Scotland. 38

43 Different from single stations, seismic arrays can provide significant signal-to-noise ratio improvement by beamforming procedures as well as robust back-azimuth and apparent velocity estimates for all types of seismic signals. The back-azimuth and apparent velocity estimates provided by seismic arrays are of great value for automatic initial determination of phase types (P, Pn, Sn, Sg/Lg), and thus facilitate stable real-time operations of network phase association and event location algorithms. Regarding signal-to-noise ratio (SNR) improvement, we show in Figure 28 an example of a small regional event in the Eastern North Sea recorded at the ESK three-component station and at the EKA array. We clearly see a significant SNR improvement for the EKA P-beam (red) and the S-beam (blue) as compared with the observation at the nearby ESK threecomponent station. Figure 28. The upper trace (blue) shows the EKA P-beam and the second trace (red) the S-beam for an event in the Eastern North Sea. The third trace shows the observation at one of the EKA array sensors (EKB1_BHZ). The three lower traces show the observation at the nearby ESK three-component station currently used in the operations of the NNSN. All traces are filtered in the 2-4 Hz band, and the vertical units are for all traces ground velocity (nm/s). The main conclusions from the study are as follows: For smaller events in the North Sea region for which no seismic phases are observable on the ESK three-component station, seismic arrivals may nevertheless be observable on the EKA array beams. The array beams formed with EKA data give significant SNR improvements, thus enabling more precise phase arrival time estimates. The EKA array has on an experimental basis been included in the automatic data processing at NORSAR and integrated with the network processing with other seismic arrays. 39

44 With EKA included, the automatic NORSAR event list contains additional small events in the North Sea region currently not being analyzed interactively. Thus, the inclusion of the EKA array would contribute to a more complete reviewed seismic bulletin. 40

45 6 Publications and presentations of NNSN data during 2014 Data collected on Norwegian seismic stations are made available through the Internet and is provided on request to interested parties. Therefore it is difficult to get a comprehensive overview on the use and all publication based on Norwegian data. The following reference list shows publications and presentations of UiB and NORSAR scientists for the reporting period, based on data of NNSN and NORSAR stations. 6.1 Publications Rodríguez-Pérez, Q. and L.Ottemöller. Source study of the Jan Mayen transform fault strikeslip earthquakes, Tectonophysics, 628, 71-84, Reports Fyen, J., Roth, M., Larsen P.W., NORSAR Scientific Report, , IS37 Infrasound station in Bardufoss, Norway, 29-39, Kjeller, Norway, June 2014 Ringdal, F., Kværna, T., Schweitzer, J., Experimental inclusion of the Eskdalemuir array in the automatic regional array processing system at NORSAR Semiannual Technical Summary, 1 January 30 June 2014, NORSAR Scientific Report, , 29-38, Kjeller, Norway, December 2014 Roth, M., Schweitzer, J., Fyen, J The modernized large-aperture broadband array NOA Semiannual Technical Summary, 1 January 30 June 2014, NORSAR Scientific Report, , 39-53, Kjeller, Norway, December Oral presentations Demuth, A. Temperature and melt regime underneath the Knipovich Rigde Seismic evidence for along-axis variations of lithospheric thickness. The 44 th Nordic Seismology Seminar, Bergen, Norway, September Junek, W.N., Kværna, T., Pirli, M., Schweitzer, J., Harris, D.B., Dodge, D.A., Woods, M.T., Vandermark, T.F., Examination of the Storfjorden aftershock sequence, Seism. Res. Lett., 85, 550, 2014 (abstract). Kvaerna, T., Schweitzer, J., Antonovskaya, G., Kremenetskaya, E.O., Enhanced earthquake monitoring of the European Arctic 11. EGU General Assembly Conference Abstracts, 16, EGU , 2014 (abstract) Schweitzer, J., D-ARCTIC The Seismological Component; NORSAR s Database, Model Status, New Projects 4DARCTIC Project Workshop, Novosibirsk, February 2014 Schweitzer, J., The NORRUSS project: GEOPROC Seismological research related to geophysical processes in the European Arctic Kick-off meeting of the NORRUSS project, NORSAR, Kjeller, 7 11 April

46 Schweitzer, J., Fyen, J., Roth, M., 2014.NORSAR s modernized, large-aperture broadband array PS27-NOA, Norway VIII International Conference, Monitoring of Nuclear Tests and Their Consequences, 4 8 August 2014, Kurchatov, Kazakhstan Schweitzer, J., Fyen, J., Kværna, T., Mykkeltveit, S., Roth, M., NORSAR 45 years monitoring the Earth, NGFs årsmøte symposium i Oslo 17 / 18 September Poster presentations Albaric, J., Hillers, G., Kühn, D., Harris, D., Brenguier, F., Ohrnberger, M.,Oye, V., 2014 Analysis of ambient seismic noise at Svalbard, poster at the 2nd European Conference on Earthquake Engineering and Seismology, Istanbul, Turkey, August 2014 Albaric, J., Hillers, G., Kühn, D., Harris, D., Brenguier, F., Ohrnberger, M.,Oye, V., 2014 Ambient seismic noise analysis from array and borehole networks in Svalbard, Norway, PSP06, poster at the EAGE 5th Passive Seismic Workshop, Lisbon, Portugal, 28 September 01 October 2014 Junek, W.N., Kværna, T., Pirli, M., Schweitzer, J., Harris, D.B., Dodge, D.A., Woods, M.T., Vandermark, T.F., Examination of the Storfjorden aftershock sequence, Seism. Soc. Amer. Annual Meeting, Anchorage, Alaska, April/May 2014 (poster) Kühn, D., Oye, V., Albaric, J., Harris, D., Hillers, G., Braathen, A., Olaussen, S., 2014 Preparing for CO2 storage in the Arctic Assessing background seismic activity and noise characteristics at the CO2 Lab site, Svalbard, poster at the GHGT-12, Austin, Texas, USA, 5 9 October 2014 Kvaerna, T., Schweitzer, J., Antonovskaya, G., Kremenetskaya, E.O., 2014.Enhanced Earthquake Monitoring of the European Arctic 11. EGU General Assembly, Vienna, April 2014 (poster) Kværna, T., Gibbons, S., Fyen, J., Roth, M., I37NO: an IMS infrasound array in northern Norway for optimal monitoring of infrasound on global and regional scales, EGU General Assembly, Vienna, April 2014 (poster) Ohrnberger, M., Hammer, C., Schweitzer, J., Temporal variability of frequencywavenumber patterns at Spitsbergen broadband array 2ECEES, Istanbul, August 2014 (poster) 42

47 7 References Alsaker A., Kvamme, L.B., Hansen, R.A., Dahle, A. and Bungum, H. (1991): The ML scale in Norway. Bull. Seism. Soc. Am., Vol. 81, No. 2, pp Andersen K. (1987): Local seismicity and volcanism in the Jan Mayen area. McS., Department of geosciences, University of Bergen. Atakan,K., Lindholm,C.D., and Havskov,J Earthquake swarm in Steigen, northern Norway: An unusual example of intraplate seismicity. Terra Nova 6, Brune J.N. (1970): Tectonic stress and spectra of seismic shear waves. Journal of Geophysical Research, 75, Grünthal, G. (1998): "European Macroseismic Scale 1998". Cahiers du Centre Européen de Géodynamique et de Séismologie Volume 15, Luxembourg. Havskov J., and Bungum, H. (1987): Source parameters for earthquakes in the northern North Sea. Norsk Geologisk Tidskrift,Vol.67, pp Havskov, J. and Ottemöller, L. (1999): SEISAN earthquake analysis software. Seism. Res. Letters, Vol. 70, pp Havskov, J. and Ottemöller, L. (2001): SEISAN: The earthquake analysis software. Manual for SEISAN v. 8.0, Department of Earth Science, University of Bergen, Norway. Havskov, J. and Sørensen, M.B. (2006): New coda magnitude scales for mainland Norway and the Jan mayen region. NNSN Technical report no. 19. Hicks, E.C., H. Bungum and C. Lindholm, Seismic activity, inferred crustal stresses and seismotectonics in the Rana region, Northern Norway, Quaternary Science Reviews 19, , 2000). Hicks, E.C. and L. Ottemöller, The M L Stord/Bømlo, southwestern Norway, earthquake of August 12, 2000, Norsk Geologisk Tidsskrift (Norwegian Journal of Geology), 81, , Kanamori, H. (1977): The energy release in great earthquakes. Journal of Geophysicsl Research 82; 20, pp Karnik, V., Kondorskaya, N.V., Riznichenko, Y. V., Savarensky, Y. F., Solovev, S.L., Shebalin, N.V., Vanek, J. and Zatopek, A. (1962): Standardisation of the earthquake magnitude scales. Studia Geophys. et Geod., Vol. 6, pp Kennett, B.L.N. and Engdahl, E.R. (1991): Traveltimes for global earthquake location and phase identification. Geophys. J. Int., Vol. 105, pp Kissling, E., W.L. Ellsworth, D. Eberhart-Phillips and U. Kradolfer (1994). Initial reference models in local earthquake tomography. J. Geophys. Res., 99, 19, ,

48 Kradolfer, U. (1996): AuroDRM The First Five Years. Seismological Research Letters, vol. 67, no. 4, Lienert, B.R. and Havskov, J. (1995): HYPOCENTER 3.2 A computer program for locating earthquakes locally, regionally and globally. Seismological Research Letters, Vol. 66, Mayeda, K., A. Hofstetter, J. L. O Boyle and W.R. Walter (2003). Stable and Transportable Regional Magnitudes Based on Coda-Derived Moment-Rate Spectra. Bull. Seism. Soc. Am,. 93, Moreno, B, Ottemöller, L., Havskov, J. and Olesen, K.A. (2002): Seisweb: A Client-Server- Architecture-Based Interactive Processing Tool for Earthquake Analysis. Seism. Res. Letters. Vol.73, No.1. Ottemöller, L. (1995): Explosion filtering for Scandinavia. Technical Report No. 2, Institute of Solid Earth Physics, University of Bergen, Norway. Pirli, M., Schweitzer, J., Ottemöller, L., Raeesi, M., Mjelde, R., Atakan, K., Guterch, A., Gibbons, S. J., Paulsen, B., Debski, W., Wiejacz, P. and Kvaerna T. Preliminary Analysis of the 21 February 2008 Svalbard (Norway) Seismic Sequence, Seismological Research Letters, 81: 63-75, Rawlinson, N. and M. Sambridge (2005). The fast marching method: an effective tool for tomographic imaging and tracking multiple phases in complex layered media. Exploration Geophysics, 36 (4), Sato, H., M. C. Fehler and T. Maeda (2009). Seismic wave propagation and scattering in the heterogeneous Earth. Chapter 2.4, Scattering of high-frequency seismic waves. Springer-Verlag Berlin Heidelberg Schweitzer, J. The 21 July 2011 earthquake in Hedmark, Southern Norway Semiannual Technical Summary, 1 January 30 June 2011, NORSAR Scientific Report, , 44-50, Kjeller, Norway, Sørensen, M.B., Ottemöller, L., Havskov, J., and Atakan, K., Hellevang, B., Pedersen, R.B Tectonic processes in the Jan Mayen Fracture Zone based on earthquake occurrence and bathymetry. Bulletin of the Seismological Society of America, Vol.97 No.3, , doi: / Veith K.F., and Clawson, G.E. (1972): Magnitude from short-period P-wave data. Bull. Seism. Soc. Am., Vol. 62, pp Waldhauser F. and W.L. Ellsworth, A double-difference earthquake location algorithm: Method and application to the northern Hayward fault, Bull. Seism. Soc. Am., 90, , Westre S. (1975): Richter's lokale magnitude og total signal varighet for lokale jordskjelv på Jan Mayen. Cand. real thesis., Seismological Observatory, University of Bergen, Norway. 44

49

50 APPENDIX 1 The NORSAR Regional Arrays

51 The NORSAR Stations and Arrays NORSAR is operating the following installations: NOA (southern Norway, array, 42 sites, 7 3C broadband sensors and 35 vertical broadband sensors) ARCES (Finmark, array, 25 sites, 25 3C broadband seismic sensors 80 Hz) SPITS (Spitsbergen, array, 9 sites, 6 3C broadband sensors and 3 vertical broadband sensors) NORES (Hedmark, array, 9 3C short-period sensors, 9 infrasound sensors) JMIC (Jan Mayen, 3C broadband sensor ) AKN (Åknes, Møre og Romsdal, 3C broadband sensor) TROLL (Antarctica, 3C broadband sensor) IS37 (Bardufoss, infrasound array, 10 sites) JETT (Jettan, Troms, 3C broadband sensor) In addition NORSAR receives and processes data in near realtime from: FINES (southern Finland, array, 16 sites, 2 3C broadband sensor, 1 3C short-period sensor and 15 short-period vertical sensors, operated by Institute of Seismology, Helsinki, Finland) HFS (Hagfors, Sweden, 10 sites, 1 3C broadband sensor and 9 short-period vertical sensors, operated by the Swedish Defence Reseearch Agency, Stockholm, Sweden) EKA (Eskdalemuir, United Kingdom, 20 sites, 1 3C broadband sensor and 20 shortperiod vertical sensors, operated by the United Kingdom National Data Centre, AWE Blacknest, UK) All NORSAR waveform data and parametric data are openly available and can be accessed through web-interfaces or direct means. The NORSAR webpage provides access to general station information, to automatic and reviewed seismic bulletins, to realtime plots of short and long-period data, and to an AutoDRM request form for waveform data retrieval. The seismic array data are automatically processed and analysed. The fastest near realtime process Automatic Alert is based on single array detection and provides event locations within a few (1-3) minutes delay. The alerts with event and location details are published immediately on (which is also integrated into the NNSN website). A second automatic process called GBF (Generalized Beam Forming) awaits for automatic phase picks from all arrays and delivers more reliable/accurate results within up to a few hours delay. Automatically processed seismic events with magnitude larger than 2 (or 1.5 if the event is of special interest) are manually analysed and reviewed. In this step all available waveforms (also from single stations) are utilized. Graphical displays and parametric event data and for Automatic Alert, GBF and Reviewed bulletins can be found on

52 NORSAR seismic arrays/stations (NOA, NORES, ARCES, SPITS, JMIC, AKN) and contributing arrays/stations (HFS, FINES, EKA, BRBA, APA).

53 Map of all stations providing realtime data to NORSAR (red/pink symbols: stations operated by NORSAR, green symbols: stations operated by of University of Bergen, yellow symbols: other cooperating/contributing stations). 1 News a) The ARCES array had a major upgrade in September We replaced sensors, digitizers at each of the 25 sites and installed a new central acquisition system. In order to minimize data loss and to keep continuity the replacement was made during a

54 time window of 3 days having old and new systems operational in parallel. All 25 sites have now three-component broadband sensors with hybrid response function), and we are sampling at 80 Hz. The hybrid response function allows us to be very sensitive in the medium-high frequency range (essential for the test ban treaty monitoring), but also not to clip in the case of large far-regional and global earthquakes. Old (dashed) an new (solid lines) instrument response fuctions at the ARCES array b) In November 2014 we installed a new station JETT at Jettan, Troms. The main purpose of the station is to monitor local seismicity associated with the unstable rock slope of the Nordnesfjellet. The instrument is a 3C Guralp ESPC with a bandwidth from 60s 100Hz. We are sampling at 200 and 40 Hz. The station is permanent and has been fully integrated into the NORSAR network. Data are forwarded in realtime to Orfeus and to NNSN.

55 New site JETT at Nordnes, Troms c) We replaced the old digitizer of our Jan Mayen station with a new Guralp embedded acquisition module in May This resolved the problems of choppy data (uncomplete backfills) during periods of poor satellite communication. d) We experimentally included the Eskdalemuir array into the automatic regional array processing system at NORSAR (Ringdal et al., 2014, Annex N-A). e) We determined 1D velocity models for the northern and southern on-shore parts of Norway, conducted resolution test for 3D tomography and established 3D models for both regions (Annex N-B). 2 Data availability All data recorded at NORSAR are continuous. The following table provides a monthly overview on the data availability of 13 main data streams provided by NORSAR to NNSN. ARE0/ARA0 JMIC NAO01 NB201 NBO00 NC204 NC303 Jan Feb Mar Apr May Jun Jul