Generic precursors to coastal earthquakes: Inferences from Denali fault earthquake

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1 Tectonophysics 431 (2007) Generic precursors to coastal earthquakes: Inferences from Denali fault earthquake Ramesh P. Singh a,b,, Guido Cervone b, Vijay P. Singh a,1, Menas Kafatos b a Department of Civil Engineering, Indian Institute of Technology, Kanpur , India b CEOSR, School of Computational Sciences, George Mason University, Fairfax, VA 22030, USA Received 25 February 2006; received in revised form 30 April 2006; accepted 15 May 2006 Available online 5 December 2006 Abstract Recent research has shown evidence of strong coupling between the atmosphere and lithosphere in coastal regions, associating abnormal atmospheric phenomena to the occurrence of strong earthquakes. Surface latent heat flux (SLHF), total column water vapor (CWV), relative humidity (RH) and total ozone column (TOC), analyzed over the epicentral region of the Denali fault earthquake of November 3, 2002, exhibit anomalous behavior that could be related to the earthquake preparatory process and its occurrence. The complementary nature of the parameters provides strong support that the anomalous values were driven by lithospheric processes, rather than other atmospheric phenomena. Due to the wide availability of remote sensing observations of atmospheric parameters, the detection of anomalies can be used to mitigate the earthquake risks Elsevier B.V. All rights reserved. Keywords: Denali earthquake; Surface latent heat flux; Ozone; Precursor 1. Introduction Earthquakes usually occur in known areas, and although it is possible to predict where an earthquake is most likely to occur, it is very complex to determine when an event will strike in a specific location. Several warning signals have been observed prior to interplate and intraplate earthquakes, usually close to the epicentral region (Hadjicontis and Mavromatou, 1994; Merzer and Klemperer, 1997; Eftaxias et al., 2001; Pham and Geller, 2002). In the last few decades several electromagnetic precursors were investigated by groups from various parts of the world, covering a wide range of frequencies from DC- Corresponding author. Department of Civil Engineering, Indian Institute of Technology, Kanpur , India. address: rsingh3@gmu.edu (R.P. Singh). 1 Now at Institut Franais du Ptrole Exploration Production Business, Unit, Paris, France. ULF, ELH, VLF, LF up to VHF (Blanc, 1985; Parrot et al., 1993; Molchanov et al., 1993; Hayakawa and Fujinawa, 1994; Biagi et al., 2001; Artru et al., 2001; Eftaxias et al., 2001). Efforts have been made to use these precursors for short-term earthquake predictions (Merzer and Klemperer, 1997). As more data are collected globally, and as new theories are formulated to explain the processes that govern earthquakes, many people believe that precursory signals can give precise information on when and where earthquakes will strike. In fact, a more positive trend is now widely spread within the community. The long term and globally collected data have provided evidence that the stress accumulating mechanisms produce electromagnetic (EM) emission of various frequencies (Artru et al., 2001) as a result displacement and deformation of surface around the earthquake source zone. Since last two decades telemetering network /$ - see front matter 2006 Elsevier B.V. All rights reserved. doi: /j.tecto

2 232 R.P. Singh et al. / Tectonophysics 431 (2007) measurements of transient variations of electric field (seismic electric signals SES) have been made in Greece and good correlation of these signals prior to impending earthquakes have been found (Merzer and Klemperer, 1997; Hayakawa and Fujinawa, 1999). The changes obtained in the electric field associated with earthquakes were supported by numerous laboratory measurements (Gokhberg et al., 1982). High electric fields have been found over seismically active regions few days prior to a strong earthquake which was thought to penetrate into ionosphere and create specific irregularities of electron concentrations over the active regions. It was believed that such irregularities in ionosphere could be measured onboard the satellite (Parrot et al., 2000). In the present paper, the analysis of atmospheric parameters retrieved from the satellite and ground measurements over the epicentre of Denali fault earthquake of November 3, 2002 is presented. The Denali fault earthquake (Mw=7.9) of November 3, 2002 was the largest strike slip earthquake (Eberhart-Phillips et al., 2003) that occurred in North America in almost 150 years. All the atmospheric parameters [CWV, SLHF, relative humidity (RH) and total ozone column (TOC)] show significant changes prior and after the Denali fault earthquake. 2. Data used The SLHF, CWV and RH data have been taken from National Centre for Environmental Prediction (NCEP) site ( The SLHF and CWV data set is available since 1949 and RH data set Fig. 1. (A) Distribution of SLHF anomaly on October 29, 2002 over epicenter and surrounding regions (star is showing location of the main earthquake event. (B) Distribution of CWVanomaly on October 30, 2002 over epicenter and surrounding regions (star is showing location of the main earthquake event. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

3 R.P. Singh et al. / Tectonophysics 431 (2007) Fig. 1 (continued). is available only from The daily average TOC data have been taken for Denali, Alaska (longitude W and latitude N) which is close to the epicenter of the Denali earthquake of November 3, The TOMS data is taken from TOMS web site ( gov). The data set available from NCEP is represented by the Gaussian grid of 94 lines from equator to pole with a regular 1.8 longitudinal spacing. The dataset is projected into a 2 2 grid size. The validation and upgrading of the database at NCEP have been discussed by Kalnay et al. (1996). Recently, the role of satellite sensors in continuous monitoring of earth, ocean and atmosphere has gained importance. 3. Results and discussion Experiments were performed using SLHF and CWV data over the region bounded by 55 N to 71 N and from 155 W to 139 W from 1 January 1998 to 31 December Fig. 1A,B show the contours of SLHF anomaly and Fig. 1C shows contours of the CWV anomaly [(SLHF/CWV value average values of SLHF/CWV of that month for 5 years)/standard deviation] over the epicentral and surrounding regions of the Denali earthquake. The SLHF anomaly is found to be highest 5 days (29 October, 2002), and the CWV anomaly is found above the 2 sigma of the average CWV value, 6 days (28 October, 2002) prior to the main event. The CWV peak is approximately 20 kg/m 2, while the 30-day average for the same period of the year is about 8 kg/m 2, indicating an increase of 12 kg/m 2, or 1.5 times the average CWV. The SLHF anomaly for 29 and 30 October, 2002 are shown in Fig. 1A andb.the location of the epicenter of the Denali earthquake is given with star. On the comparison of SLHF/CWV anomaly maps for a week, we have found that the

4 234 R.P. Singh et al. / Tectonophysics 431 (2007) Fig. 1 (continued). SLHF/CWV anomalies have their origin in the southeastern corner of the map, close to the continental boundaries, and migrate towards the epicentral region on the following day (Fig. 1A,B). The CWV anomaly is found to be highest over the epicenter on 29 October, 2002 (Fig. 1C). Fig. 2A,B, respectively show the yearly variations of SLHF and CWV for the year The average of SLHF and CWV for the year for June December are also shown togetherwith1and2sigma values of SLHF and CWV. The SLHF shows anomalous value about 5 days and the anomalous values of CWVisobserved6dayspriorto the main earthquake event. This anomalous value of SLHF and CWV over the epicenter is about 4 and 5 days prior to the earthquake event (3 November 2003). In Fig. 2A,B, the red circle showing maxima peaks of SLHF and CWV, respectively, which show anomalous peaks (5 days priorinslhfand6dayspriorincwv)priortothe main earthquake event. The SLHF/CWV detected singularities in the data, and the wavelet coefficients with corresponding maxima curves are shown in Fig. 2A,B. We have followed the approach of Cervone et al. (2004) to determine singularities in the data, or sudden changes in the first derivative of the SLHF/CWV data. The value of the SLHF peak is approximately 50 W/m 2 and the 30-day average is about 20 W/m 2. This indicates an increase of 30 W/m 2, or 1.5 times higher than the average SLHF (Fig. 2A). Fig. 2B shows the wavelet transformation of the CWV Water signal. A prominent CWV peak 6 days prior to the main earthquake event is found well above the 2 sigma CWV value. The CWV peak is approximately

5 R.P. Singh et al. / Tectonophysics 431 (2007) kg/m 2, while the 30-day average for the same period of the year is about 8 kg/m 2, indicating an increase of 12 kg/m 2, or 1.5 times the average CWV. The SLHF and CWV are also found to be dependent on the distance of the location from the ocean, wind, surface temperature, relative humidity and contrast Fig. 2. (A) Time series of SLHF for the year 2002 (upper panel) and wavelet of SLHF signal for the year 2002 (lower panel), the dash line shows the day of earthquake event. (B) Time series of CWV for the year 2002 (upper panel) and wavelet of CWV signal for the year 2002 (lower panel), the dash line shows the day of earthquake event. (C) Continuity of SLHF signal along grids shown in Fig. 1A. Only three maxima SLHF signals are found to show maximum continuity among three only the SLHF signal 5 days prior to the main earthquake shows maximum continuity through grids with higher magnitude of SLHF which is considered as earthquake precursor. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

6 236 R.P. Singh et al. / Tectonophysics 431 (2007) Fig. 2 (continued). between the surface and air temperature of a particular day (Dey and Singh, 2003; Gautam et al., 2004). The SLHF shows a maxima peak associated with Denali fault earthquake 5 days prior to November 3, 2002 (the day when earthquake occurred) (Fig. 2A). The CWV is found to be maximum 6 days prior to earthquake on November 3, 2002 (Fig. 2B) and the relative humidity (RH) is found to be maximum 6 days prior to the earthquake on November 3, 2002 (Fig. 4A). The maxima peaks of water vapor increases by 25.2%, SLHF by 27.8% and RH by 41%, respectively, 6, 5 and 6 days prior to the earthquake occurrence from the maximum background noise observed in the last 5 years. The maxima peaks of these parameters are

7 R.P. Singh et al. / Tectonophysics 431 (2007) Fig. 2 (continued). very clearly distinguished from the background noise of total CWVand SLHF. It can be said that the anomalous maxima peaks are associated with the earthquake that occurred on November 3, There were many aftershocks after the main earthquake event and small changes in SLHF and CWV are likely to be related to these aftershocks. The anomalous increase of these parameters prior to the main earthquake, foreshocks and aftershocks are plausible with the increase of ground temperature associated with the driving stress on the fault (Chandra et al., 1998; Kanamori, 1998). The increase of temperature may give rise to the increase of evaporation from the epicentral region and adjacent ocean leading to the increase of CWV (Fig. 1B) and RH (Fig. 4A) about 6 days prior to the earthquake and is likely related to the increase of SLHF (27.8%, 1 day after the increase of CWV and RH i.e. 5 days prior to the earthquake). In Fig. 4A, the dotted thick bar represents the day of the main earthquake event whereas thin solid bars shows the one foreshock

8 238 R.P. Singh et al. / Tectonophysics 431 (2007) Fig. 3. Surface temperature at Fairbanks for the years (A) 2000, (B) 2001 and (C) Six days prior to the main earthquake the surface temperature is found to be higher (red circle). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) (Ms=6.8) on October 23, 2002 and one aftershock (Ms=5.2) (November 14, 2002). From Fig. 2A, one can see that significant maxima peaks above 2 sigma during Not all the SLHF are associated with the earthquakes. The SLHF peaks are associated with the atmospheric disturbances and many other parameters. Recently, Cervone et al. (2004) have found that the SLHF associated with

9 R.P. Singh et al. / Tectonophysics 431 (2007) Fig. 4. (A) Variations of relative humidity for the period October November, The solid bar dark shows the day of the main earthquake and thin solid line shows the days of foreshock and aftershock. (B) Variations of TOC during October November earthquakes show continuity through maximum grids whereas the SLHF associated with the atmospheric perturbations are of local nature. Fig. 2A shows 6 7 maxima SLHF peaks beyond 2 sigma but only three peaks are found to show of higher magnitude which follow continuity along grids. Fig. 2C shows the results of the analysis of continuity performed using grids 33, 34, 35, 36, 29, 30, 23 and 24 (Fig. 1A). The space/time continuity along the selected grids of the anomalies detected by the wavelet transformation is shown in Fig. 2C. The x axis represents days, and the y axis represents different grids. A straight vertical line indicates a signal which exhibits both space and time continuity, since it occurs along all the grids at the same time. Three prominent signals were identified, one of which is occurring 5 days prior to the earthquake event. The anomaly detected through wavelet transformation and illustrated in Fig. 2A is not localized only at the epicenter, but it extends several kilometers to the east and to the west, along the major fault lines of the region, parallel to the continental boundary. The SLHF signal 5 days prior to the earthquake is found to be of very high magnitude which shows maximum continuity. This signal provides information about the main Denali fault earthquake event which occurred on November 3, The surface temperature data for Fairbanks (longitude W, latitude N) which is close to the epicentre of Denali earthquake is shown in Fig. 3A C for the years The surface temperature data clearly show anomalous increase of surface temperature (shown by circle, Fig. 3C) prior to the earthquake (solid bar showing earthquake event), normally the surface temperature during October December is below freezing temperature (Fig. 3A and B). In the year 2002, due to the Denali earthquake, the surface temperature crossed the freezing temperature (Fig. 3C). The increase of these atmospheric parameters is also found to be associated with the total ozone column (TOC; data is taken from TOMS web site gsfc.nasa.gov) after the earthquake (Fig. 4B). The TOC is found to show increasing trend after the earthquake. The increase of TOC is associated with the decrease in CWV after the earthquake in the epicentral region and is likely associated with suppressed convection and downward motion (Valero et al., 1997). 4. Conclusion The present result shows that the anomalous increase of surface temperature (minimum and maximum), CWV,

10 240 R.P. Singh et al. / Tectonophysics 431 (2007) SLHF, RH and TOC in the atmosphere are closely associated with the Denali fault earthquake. The changes in CWV, SLHF and RH are likely to be associated with the increase of surface temperature which are basically controlled by the stress generated along the fault prior to the earthquake. All the atmospheric parameters show a strong linkage which is quite consistent. The CWV and SLHF anomalies 5 6 days prior to the Denali fault earthquake clearly provide information about an impending earthquake. The changes in relative humidity are also found to be consistent with the changes in CWV and SLHF. Detailed analysis of SLHF and CWV over the epicentres of 40 coastal earthquakes which occurred throughout the globe during have also been carried out and similar characteristics of CWV and SLHF about 1 14 days prior to the earthquakes have been observed. The analysis of SLHF and CWV over the epicenters of earthquakes occurred far from the ocean did not show such characteristics behavior. The SLHF and CWV are found to be reliable precursors for coastal earthquakes which provide information about 1 14 days prior to an impending earthquake (Cervone et al., 2006). The background noise level in CWV is usually large compared to SLHF although the increase in CWV and SLHF are consistent and diagnostic. Acknowledgement The surface latent heat flux (SLHF) has been taken from the National Center for Environmental Prediction (NCEP) website ( The data has been downloaded from the Scientific Computing Division of the National Center for Atmospheric Research (NCAR) website [ edu/sources/noaa/ncep-ncar/]. The authors are grateful to Ms. Julia Lenz, Alaska State Climate Center, Fairbanks for her help in providing climatological data. The authors are grateful to Dr. Michael E. 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