Preliminary Earthquake Report

Transcription

1 THE UNIVERSITY OF THE WEST INDIES ST. AUGUSTINE, TRINIDAD AND TOBAGO, WEST INDIES THE SEISMIC RESEARCH CENTRE Telephone: (868) Website: Preliminary Earthquake Report UTC Mt 5.5 STRONG MOTION PARAMETERS FOR PORT OF SPAIN FROM LOCAL STRONG MOTION NETWORK & INTENSITY REPORT FROM CITIZEN SEISMOLOGIST COMMUNITY PROJECT Ilias Papadopoulos, Celeste Sobion & Hannah Ramsingh Tel: ; Fax: /07/05

2 The results of the present report are preliminary and may be subject to revision if more detailed analyses will be carried out. The uncorrected data of the records in ASCII are available upon request. DISCLAIMER This report was compiled by the Engineering Seismologist of The University of the West Indies Seismic Research Centre Ilias Papadopoulos. The accuracy and credibility of the results and the opinions expressed in this report are solely his and do not necessary reflect those of the Centre.

3 Contents Summary... 4 Earthquake Parameters (Source: UWI SRC)... 5 Port of Spain General Hospital (PSGH)... 6 Strong Motion Parameters... 7 Elastic Response Spectra (SA)... 8 Fourier Amplitude Spectra... 9 PSGH Particle Motion Comparison with IBC2000 Design Spectra Kent House (PSKH) Strong Motion Parameters Elastic Response Spectra Fourier Amplitude Spectra PSKH Particle Motion Comparison with IBC2000 Design Spectra Mucurapo Girls RC (PSMG) Strong Motion Parameters Elastic Response Spectra (SA) Fourier Amplitude Spectra PSMG Particle Motion Comparison with IBC2000 Design Spectra Woodbrook Secondary (PSWS) Strong Motion Parameters Elastic Response Spectra (SA) Fourier Amplitude Spectra PSWS Particle Motion Comparison with IBC2000 Design Spectra Analysis of the Citizen Seismologist Community Project Felt Reports Demographics Perception of Seismic Shaking Intensity... 29

4 Summary This document serves as a preliminary report for the moderate earthquake occurred in 2018/06/22, 01:54 UTC (21:54 local time) northwest of Trinidad (Coordinates N, W) (source:src). Its focal depth of Km allowed the shaking to be felt to a wider area. The Port of Spain Strong Motion Network (POS SMN) recorded the event, and the strong motion data processing appears in this document. At the second section of this document the intensity report is presented, as recorded by the SRC s Citizen Seismologist Community Project. The maximum instrumentally recorded PGA value in the area of Port of Spain is recorded in Maraval, at station PSKH (PGA= m/s 2 ), while the highest intensity values in Modified Mercalli Intensity (MMI) Scale appear in reports from Maraval, Woodbrook and St. James (MMI=V). There have been no reports of casualties or damages. Initial results indicate that the western part of Port of Spain experienced higher seismic intensity compared to the eastern side. This appears both in the instrumental recorded waveforms and community felt reports. The geophysical survey conducted by SRC the past years in Port of Spain shows the western part to have a thicker package of sediments compared to the eastern side, while the geological survey shows that the soil deposits of the eastern side are more compacted. The areas of St. Claire, Woodbrook and St. James are the natural flood plains of the Maraval River and the water table of the underground aquifer appears at shallower depths at the west (less than 1m). All these indicate that the western side of Port of Spain is to experience higher levels of shaking, especially as it gets closer to the coast, where also reclamation has been conducted in the past. Station PSWS, located at Woodbrook Secondary School, experienced a short break in transmission of data, creating a gap in data recorded in the vertical component. We were unable to retrieve the whole waveform for this component from that station, hence the results for this component are incomplete.

5 SECTION 1 STRONG MOTION PARAMETERS Earthquake Parameters (Source: UWI SRC) Date Time 0154 UTC Latitude N Longitude W Depth km Magnitude (Mt) 5.5 Mean Epicentral Distance from POS SMN 92.5 Km Mean Hypocetral Distance from POS SMN Km Mean Azimouth 98 o Figure 1. Google image showing the location of the earthquake event on June 6 th, UTC.

6 Port of Spain General Hospital (PSGH) Port of Spain General Hospital (PSGH) Longitude W Soil Type Soft Latitude N Vs 30 (m/s) 420 Elevation (m) 15.5 NEHRP Class C Building Structure Wood Resonance Frequency 2.2 Installation Surface/Concrete Sensor Guralp 5TDE Telemetry Internet/Wired Digitizer Guralp DM24 Mean PGA (m/s 2 ) Mean Period (s) Figure 2. PSGH unfiltered waveform (Z: Vertical; N: North-South; E: East-West). Units in m/s 2.

7 Strong Motion Parameters Figure 3. Strong Motion Parameters (Top); Time Histories, unfiltered (Bottom). Units: a (m/s 2 ), V (cm/s), D (cm)

8 Elastic Response Spectra (SA) Figure 4. Elastic Response Spectra. SA (top left), SV (bottom left), SD (top right) & all damping. Units: SA (m/s 2 ), SV (cm/s), SD (cm). Components: Z: Vertical; N: North-South; E: East-West.

9 Fourier Amplitude Spectra Figure 5. Fourier Amplitude Spectrum, three components and summary. Comparison between noise & signal (top), signal-to-noise ratio (bottom). Components: Z: Vertical; N: North-South; E: East-West..

10 PSGH Particle Motion Figure 6. Particle motion, horizontal plane. Comparison with IBC2000 Design Spectra Figure 7. Comparison of elastic response spectra damping with IBC2000 Design Spectrum.

11 Kent House (PSKH) Kent House (PSKH) Longitude W Soil Type Soft Latitude N Vs 30 (m/s) 440 Elevation (m) 25.4 NEHRP Class C Building Structure Free Field Resonance Frequency 3.2 Installation Surface/Concrete Sensor Guralp 5TDE Telemetry Internet/Wired Digitizer Guralp DM24 Mean PGA (m/s 2 ) Mean Period (s) Figure 8. PSKH recording (Z: Vertical; N: North-South; E: East-West). Units in m/s 2.

12 Strong Motion Parameters Figure 9. Strong Motion Parameters (Top); Time Histories, unfiltered (Bottom). Units: a (m/s 2 ), V (cm/s), D (cm)

13 Elastic Response Spectra Figure 10. Elastic Response Spectrum, Units: Units: SA (cm/s 2 ), SV (cm/s), SD (cm). Components: Z: Vertical; N: North-South; E: East-West.

14 Fourier Amplitude Spectra Figure 11. Fourier Amplitude Spectrum, three components and summary. Comparison between noise & signal (top), signal-to-noise ratio (bottom). Components: Z: Vertical; N: North-South; E: East-West..

15 PSKH Particle Motion Figure 12. Particle motion, horizontal plane. Comparison with IBC2000 Design Spectra Figure 13. Comparison of elastic response spectra damping with IBC2000 Design Spectrum.

16 Mucurapo Girls RC (PSMG) Mucurapo Girls RC (PSMG) Longitude W Soil Type Soft Latitude N Vs 30 (m/s) 370 Elevation (m) 8.1 NEHRP Class C/D Building Structure Free Field Resonance Frequency 1.4 Installation Surface/Concrete Sensor Guralp 5TDE Telemetry Internet/Wireless Digitizer Guralp DM24 Mean PGA (m/s 2 ) Mean Period (s) Figure 14. PSMG recording (Z: Vertical; N: North-South; E: East-West). Units in m/s 2.

17 Strong Motion Parameters Figure 15. Strong Motion Parameters (Top); Time Histories, unfiltered (Bottom). Units: a (m/s 2 ), V (cm/s), D (cm)

18 Elastic Response Spectra (SA) Figure 16. Elastic Response Spectra, Units: Units: SA (m/s 2 ), SV (cm/s), SD (cm). Components: Z: Vertical; N: North-South; E: East-West.

19 Fourier Amplitude Spectra Figure 17. Fourier Amplitude Spectrum, three components and summary. Comparison between noise & signal (top), signal-to-noise ratio (bottom). Components: Z: Vertical; N: North-South; E: East-West..

20 PSMG Particle Motion Figure 18. Particle motion, horizontal plane. Comparison with IBC2000 Design Spectra Figure 19. Comparison of elastic response spectra damping with IBC2000 Design Spectrum.

21 Woodbrook Secondary (PSWS) Woodbrook Secondary (PSWS) Longitude W Soil Type Soft Latitude N Vs 30 (m/s) 363 Elevation (m) 5.5 NEHRP Class C/D Building Structure Reinforced Concrete Resonance Frequency 0.9 Installation Surface/Concrete Sensor Guralp 5TDE Telemetry Internet/Wireless Digitizer Guralp DM24 Mean PGA (m/s 2 ) Mean Period (s) Figure 20. PSWS recording (Z: Vertical; N: North-South; E: East-West). Units in m/s 2.

22 Strong Motion Parameters Figure 21. Strong Motion Parameters (Top); Time Histories, unfiltered (Bottom). Units: a (m/s 2 ), V (cm/s), D (cm)

23 Elastic Response Spectra (SA) Figure 22. Elastic Response Spectra, Units: Units: SA (m/s 2 ), SV (cm/s), SD (cm). Components: Z: Vertical; N: North-South; E: East-West.

24 Fourier Amplitude Spectra Figure 23.. Fourier Amplitude Spectrum, three components and summary. Comparison between noise & signal (top), signal-to-noise ratio (bottom). Components: Z: Vertical; N: North-South; E: East-West..

25 PSWS Particle Motion Figure 24. Particle motion, horizontal plane. Comparison with IBC2000 Design Spectra Figure 25. Comparison of elastic response spectra damping with IBC2000 Design Spectrum.

26 SECTION 2 MODIFIED MERCALLI INTENSITY REPORTS

27 Figure 26. Nationwide Modified Mercalli Intensity values. Figure 27. Port of Spain Intensity map. With green dots the POS SMN is presented. Size according to maximum recorded PGA value. Also shown is the MMI value from felt reports.

28 Analysis of the Citizen Seismologist Community Project Felt Reports Demographics Reports Demographics Submitted 346 Urban Not available Complete 346 Rural Not available Reliable 342 Female 275 Usable 90 Male 65 Comments Submitted: Total submitted online reports Complete: Reports with all fields filled Reliable: Reports considered filled with good will and faith Usable: Reports with exact location to be place on a map Urban: Total submitted reports indicating address in urban areas Rural: Total submitted reports indicating address in rural areas Female: Total submitted reports filled by female Male: Total submitted reports filled by male

29 Perception of Seismic Shaking Intensity From the statistical analysis of the reliable felt reports, the earthquake of 01:54 UTC was reported felt in 97.2% of submitted reports. Most of the reports were filled by female (81%). The majority of reports consider the earthquake shaking moderate (46%), while the shaking is described mostly as trembling or swaying (32% and 33% respectively). At the time of the event (21:54, local time) most people were awake and sitting still or laying down (88%). The event caught T&T s citizens by surprise (46%), while enough expressed fear (34%). Animals nearby (indoors and outdoors) got upset (87%). Most submissions, report light swing of hanging objects (57%), while doors, windows, china and glasses rattled (52-53%). The majority reports a sound effect (58%), which appeared before (37%) or during (60%) the ground shaking. Reports are almost equally divided in the origin of the sound effect, either from inside the building or from underground. While no significant damages are reported, a small percentage of reports indicate cracks on the wall and plaster falling from ceiling (6%). No other damage reported on walls or collapses. The biggest concern from the authors of this report, is the amount of submissions that are unusable for scientific research (74.4%), due to lack of precise location. While some citizens failed to provide an address, by negligence or typing something irrelevant (e.g. my house) or providing fewer details (e.g. Eastern Main Road), some others don t have an address to report that can be of use (e.g. Lamp Post 23, Maraval Road). Within the frame of Citizen Seismologist Community Project, an effort needs to be made for these citizens to be able to determine accurately their location, in order for SRC to use the essential information provided.

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