Comprehensive Geomagnetic Signal Processings for Sucessful Earthquake Prediction

Transcription

1 Comprehensive Geomagnetic Signal Processings for Sucessful Earthquake Prediction Teti Zubaidah, Bulkis Kanata, Cipta Ramadhani Jurusan Teknik Elektro, Fakultas Teknik - Universitas Mataram Jl. Majapahit 62, Mataram 83125, INDONESIA tetizubaidah@te.ftunram.ac.id uqikanata@te.ftunram.ac.id cipta@te.ftunram.ac.id Abstract Previous studies suggested that seismoelectromagnetic signals were generated during earthquake preparation phase. While the anomalous signals in Japan, Russia, and Greece are rather clear; observational results in some regions including America and Indonesian have not conclusive yet, whether the signals are really exist or normal magnetic storm phenomena only. Some problems in measuring instrumentations might also result in anomalous signals. This paper reviews further possibilities by processing a nearly continuous geomagnetic data of INTERMAGNET observatories in three regions (Japan, America, and Indonesia) during the last twelve years ( ). MATLAB with digital signal processing and statistical toolboxes is used for night-time data filtering, thereafter processing methods of differentiation and moving average are applied. To get relationship between these anomalous signals and natural processes, tectonic settings of the regions and global geomagnetic conditions are also considered in the analysis. Fast decreasing of geomagnetic intensities signals are showed prior to earthquakes in Japanese regions, while some little increases of differentiation signals between two adjacent observatories were seen from their moving average values. The anomaly was nt, during 8 days started from 32 days prior to the earthquake. Decreasing of geomagnetic intensities prior to earthquakes in American regions occurred rather longer and formerly (during 40 days started from 137 days prior to the earthquake), but the magnitudes are not so high. In Indonesian regions, fast decreasing of geomagnetic signals and increasing of differentiation signals are very clear, especially prior to the giant M9.1 Sumatra earthquake. The anomaly reached extreme magnitude of more than 200 nt during several days prior to the earthquakes. All observational results are back to the normal (base line) values after earthquake occurrences. The distances from the observatories to the epicenters and the magnitudes of earthquakes very affect the results. Elevations of observatories and the tectonic settings of regions may also affect the magnitude of anomalous signals. Some missing data during earthquake days are in fact very valuable to complete the analysis. After all, the geomagnetic signal processing is very valuable in searching appropriate precursors for successful earthquake predictions. Keywords Geomagnetic; earthquake; precursor; differentiation; INTERMAGNET Budi Irmawati Jurusan Teknik Informatika Fakultas Teknik - Universitas Mataram Jl. Majapahit 62, Mataram 83125, INDONESIA wati@te.ftunram.ac.id I. INTRODUCTION Earthquake occurrences are quite often reported to be preceded by some natural anomalous phenomena, among others are increasing or decreasing of regional electric and geomagnetic signals, especially Ultra Low Frequency (ULF) component. Researches on this topic, called as seismoelectromagnetic phenomena, have been conducted in various regions since early nineteenth century. However, [1] has underlined that much of the earliest work was recognized as spurious, because the transient signals were resulted from magnetic variometers (suspended magnets) and other instruments sensitive to ground displacement, acceleration, and rotation common in epicentral regions during the propagation of seismic waves. Only after the mid-1960s, these problems have been avoided through the use of absolute magnetometers installed in regions of low magnetic field gradient to reduce sensitivity to earthquake shaking and by the application of new noise reduction techniques. As a consequence, unambiguous observations of EM variations related to earthquakes and tectonic stress/strain loading, have now been obtained near active faults in many countries (Japan, China, Russia, Italy, Greece, America, and other locations). Controversies around this crucial topic are still going on. The mostly cited seismo-electromagnetic report is of [2], who accidentally detected extreme ULF geomagnetic signals transient from a ground-based instrument installed at Corralitos, just close (7 km) to the epicentrum of 1989 M7.1 Loma Prieta earthquake in California. They observed increasing of ULF geomagnetic signal amplitudes (in the frequency range of Hz) since one month prior to the earthquake, and detected strong enhancement of the Hz signals from two days before until the occurrence of the earthquake. Conversely, [3] have re-examined all of the available Corralitos data (21 months from January 1989 to October 1990), have found that the reported anomalous geomagnetic signals transient identified by [2] is not related to the Loma Prieta earthquake but is an artifact of sensor-system malfunction. Another minor opinion against seismo-electromagnetic signal analysis as earthquake precursors is of [4]. They have

2 concluded that useful prediction of damaging earthquakes seems unlikely using these electromagnetic data, based on the absence of electric and magnetic field precursors for the 2004 M6.0 Parkfield earthquake and other earthquakes with M5 7.3 elsewhere in the San Andreas fault system. Some other authors view the efforts of short term predictions of earthquakes using precursory anomalous signals with strong skepticism, while [5] even called such efforts as a magnetic fraud. Contrarily, several authors believe that someday people will be able to predict the earthquake occurrences in only a short range of days. They argued that it is just like people being able to fly with airplanes today, which was still a dream before the 19 th century. These optimistic researchers never give up to search and actively propose the appropriate methods that can be applied for middle-term and even shortterm earthquake predictions, which are suitable for regional earthquake early warning system. Among this optimistic group members are [6] and [7, 8]. Some of important efforts in searching the methods have been collected by [9] and [10]. In fact, several seismo-electromagnetic satellite-based researches have reported anomalous signal evidences detected from the sky. Changes of ULF and VLF signals in the Ionosphere were detected by the Intercosmos-19 satellite, within 2 latitude and 60 longitude from the epicenter, since 8 hours prior to -until 3 hours after- the 1979 earthquake in Russia [11]. [12] reported that ULF/VLF signals below 450 Hz were detected by COSMOS-1809 satellite, within 6 latitude from the epicenter of the 1988 earthquake in Armenia. Finally, [13] have applied wavelet analysis to investigate if electromagnetic disturbances related to the 2004 M9.2 Sumatra great earthquake could be detected by satellite magnetometers. They have concluded that only a statistical study based on large earthquakes recorded during the CHAMP magnetic mission could bring an answer to such a crucial question. Regarding all above achievements, searching appropriate methods for seismo-geomagnetic signal processing are still big challenges; because there is no single method appropriate to be applied for every case of earthquake occurrences in different regions over the entire globe. In other words, it is quite possible that each region needs a specific approach to find the most appropriate signal processing method, which depends on its geology and tectonic characteristics. This paper reports seismo-geomagnetic signal processing by applying differentiation and moving average procedure in the Japanese, American, and Indonesian regions during the last twelve years ( ). Three big earthquakes -two of them are giants- will be analyzed to know whether such earthquakes can generate anomalous geomagnetic signal fluctuations. When the anomalous signals appeared and how large the magnitude of earthquakes will affect the intensity of anomalous geomagnetic signals will also be analyzed. To get relationship between these anomalous signals and natural processes, tectonic settings of the regions and global geomagnetic conditions are also considered in the analysis. Finally, a fundamental question will be answered, whether seismo-geomagnetic signal processing are really possible to be used as earthquake precursors and applicable for hazard mitigations. II. DATA COLLECTIONS AND METHOD The geomagnetic data from the regions of Japan, USA, and Indonesian are obtained from the INTERMAGNET ( The data are of one-minute total intensity (F), which have been initially measured every second, nearly continuously along twelve years during The data of each region have to be collected from three different observatories, which surround the earthquake locations. To get the reliable data, we use only definitive one and of night time values (i.e. 00:00 06:00 of the local times). MATLAB with digital signal processing and statistical toolboxes is used for night-time data filtering, thereafter processing methods of differentiation and moving average are applied. The differentiation procedure was done to reduce signal fluctuations due to diurnal variation, ionospheric as well as magnetospheric disturbances, and to eliminate secular variations. Results will be only variations due to local lithospheric magnetizations, which might be in connection with tectonic activities. To determine how well localization of anomalous signals, observations on global geomagnetic indices were taken by evaluations of the summing of planetary index (Sigma Kp) obtained from ftp site of the Deutsches GeoForschungsZentrum (ftp://ftp.gfz-potsdam.de/pub/home/ obs/kp-ap/wdc/). The procedure of data processing has been used in [14], which can be shortly described as following: (i) The selected data from the three observatories on one region are daily averaged and plotted individually. (ii) The data are then subtracted each other, to get the differential signals between two observatories in the order of (Obs1-Obs2), (Obs1-Obs3), and (Obs2-Obs 3). (iii) The differential signals are moving averaged to get the low pass filtered (smoothed) signals, with time windows of 7 days (regarding 27 days time interval of the solar cycle). (iv) The signal trends are defined and evaluated over the elapsed times for each moving averaged results, with the focus on the time of earthquake occurrences. III. SEISMO-GEOMAGNETIC SIGNALS IN THREE REGIONS A. Japanese Region Data from three INTERMAGNET observatories in Japanese region will be used, i.e. Memambetsu (MMB), Kakioka (KAK), and Kanoya (KNY). The geographical positions of the three observatories and their distances to the earthquake epicenter are listed in Table 1, while Fig. 1 depicts their locations and the epicenter location of studied giant Tohoku Earthquake. The earthquake occurrence is on March 11th 2011 at (38.3 N, E) with M9.0 and 29 km depth. Fig. 2 shows geomagnetic data during October 2010 September 2011 from MMB, KAK, and KNY. Fig. 2(a) shows daily averaged values of the geomagnetic total intensity data, while Fig. 2(b) shows the differentiations between two

3 observatories and their moving averages. We also show the sigma Kp values to be an indicator for global geomagnetic conditions, especially prior to the earthquake occurrence. As seen on the parts marked with circles in Fig. 2, some anomalous signal clearly exist with their intensity values as calculated on Table 2. The highest anomalies are in the differentiation signals between KAK and KNY. There were four anomalous signals, with intensities of 9.06 nt on 33 days, nt on 10 days, 6.51 nt on 4 days, and 16.8 nt on 1 day prior to the earthquake. Unfortunately, no data recorded on the day of earthquake and three days after, probably because of electrical power failure. Using moving average procedure, we see clear anomalous patterns with magnitude of nt during 8 days (DOY 38 45), starting from 32 days prior to the earthquake (from DOY 70). In this case, sigma Kp values are low; means that no geomagnetic storms occurred during the anomalous days. We are, therefore, confident that the anomalous signals were local in the Japanese region and in close correlation to the earthquake occurrence. B. American Region Data from three INTERMAGNET observatories in American region will be used, i.e. Boulder (BOU), Fresno (FRN), and Tucson (TUC). The geographical positions of the three observatories and their distances to the earthquake epicentre are listed in Table 1, while Fig. 3 depicts their locations and the location of studied Colima/Mexico Earthquake. The earthquake occurrence is on January 22 nd 2003 at (18.77 N, E) with M7.6 and 24 km depth. Fig. 4 shows geomagnetic data during July 2002 June 2003 from BOU, FRN, and TUC. Fig. 4(a) shows daily averaged values of the geomagnetic total intensity data, while Fig. 4(b) shows the differentiations between two observatories and their moving averages Fig. 1. Three geomagnetic observatories and the location of studied earthquake in Japanese region: MMB, KAK, and KNY with the giant M9.0 Tohoku Earthquake on March 11th TABLE I. Regional Japan America Indonesia GEOMAGNETIC OBSERVATORIES IN JAPANESE, AMERICAN, AND CLOSE TO INDONESIAN REGION IAGA code Lat Long Elev. (m) Dist. to EQ (km) MMB N E KAK N E KNY N E BOU N E FRN N E TUC N E LRM N E KDU N E PHU N E TABLE II. INTENSITY OF ANOMALOUS GEOMAGNETIC SIGNALS ON MMB, KAK, AND KNY PRIOR TO THE TOHOKU EARTHQUAKE Anomaly (nt) DOY 37 (33 days Earthquake on (DOY 70) DOY 60 DOY 66 (10 days (4 days DOY 69 (1 day MMB-KAK MMB-KNY KAK-KNY Sigma Kp TABLE III. INTENSITY OF ANOMALOUS GEOMAGNETIC SIGNALS ON BOU, FRN, AND TUC PRIOR TO THE COLIMA/MEXICO EARTHQUAKE Anomaly (nt) DOY 206 (181 days Earthquake on (DOY 22) DOY 250 DOY 277 (137 days (110 days DOY 12 (15 day BOU-FRN BOU-TUC FRN-TUC Sigma Kp We also show the sigma Kp values to be an indicator for global geomagnetic conditions, especially prior to the earthquake occurrence. As seen on the parts marked with circles in Fig. 4, some anomalous signal clearly exist with their intensity values as calculated on Table 3. The highest anomalies are in the differentiation signals between FRN and TUC, but then between BOU and FRN. There were four anomalous signals, with intensities of nt on 181 days, nt on 137 days, nt on 110 days, and 30.0 nt on 15 days prior to the earthquake. The minus signs mean that the signals are lower than normal values. Unfortunately, no data recorded on some days prior to the earthquake, while anomalous signals were recognized. Nevertheless, by using moving average procedure, we still see the track of anomalous signals during 40 days (DOY ), starting from 137 days prior to the earthquake. In this case, sigma Kp values fluctuate, with some high in between low values. It means that geomagnetic storms probably occurred during some of the anomalous days. Therefore, we considered that not all of the anomalous signals were local in the American region, but due global geomagnetic storms. On the other hand, we are also confident that some anomalous signals were really in close correlation to the earthquake occurrence.

4 Sigma Kp Daily mean of the total magnetic field differences (nt) Daily mean of the total magnetic field (nt) 49,730 MMB 49,690 49,650 46,530 KAK 46,490 46,450 46,440 KNY 46,400 46,360 (a) 3,230 Eq(2011/03/11) M9.0 MMB-KAK MMB-KAK 7 days running average 3,190 3,320 MMB-KNY MMB-KNY 7 days running average 3, KAK-KNY KAK-KNY 7 days running average (b) Fig. 2. Geomagnetic anomalous signal related to the M9.0 giant Tohoku Earthquake on March 11th (a) The daily mean of the total geomagnetic fields observed by three observatories in Japanese region (MMB, KAK, and KNY), and (b) The differentiations signals of two observatories and the moving averages, with sigma Kp values of corresponding days to evaluate the global geomagnetic conditions. C. Indonesian Region Since no INTERMAGNET observatory in Indonesia, data from three INTERMAGNET observatories which are close to Indonesian region will be used, i.e. Learmonth (LRM) in Australia, Kakadu (KDU) in Australia, and Phuthuy (PHU) in Vietnam. The geographical positions of the three observatories and their distances to the earthquake epicenter are listed in Table 1, while Fig. 5 depicts their locations and the location of studied giant Sumatera Earthquake. The earthquake occurrence is on December 26th 2004 at (3.3 N, E) with M9.1 and 30 km depth. Another M7.5 earthquake happened before on November 11th 2004 also in Indonesian region will be used as comparison. Fig. 6 shows geomagnetic data during July 2004 December 2005 from LRM, KDU, and PHU. Fig. 6(a) shows daily averaged values of the geomagnetic total intensity data, while Fig. 6(b) shows the differentiations between two observatories and their moving averages. We also show the sigma Kp values to be an indicator for global geomagnetic conditions, especially prior to the earthquake occurrence. As seen on the parts marked with circles in Fig. 6, some anomalous signal clearly exist with their intensity values as calculated on Table 4. Unfortunately, many data were missing on some days prior to and after the earthquakes. Fig. 3. Three geomagnetic observatories and the location of studied earthquake in American region: BOU, FRN, and TUC with the M7.6 Colima/Mexico Earthquake on January 22nd 2003.

5 Sigma Kp Daily mean of the total magnetic field differences (nt) Daily mean of the total magnetic field (nt) 53,750 BOU 53,700 53,650 53,600 49,550 FRN 49,500 49,450 49,400 48,750 TUC 48,700 48,650 48,600 (a) Eq(2003/01/22) M7.6 4,240 BOU-FRN BOU-FRN 7 days running average 4,200 4,160 BOU-TUC 5,040 BOU-TUC 7 days running average 5, FRN-TUC FRN-TUC 7 days running average (b) Fig. 4. Geomagnetic anomalous signal related to the M7.6 Colima/Mexico Earthquake on January 22nd (a) The daily mean of the total geomagnetic fields observed by three observatories in American region (BOU, FRN, and TUC), and (b) The differentiations signals of two observatories and the moving averages, with sigma Kp values of corresponding days to evaluate the global geomagnetic conditions. Nevertheless, anomalies were clearly seen in the differentiation signal between LRM and PHU. There were four anomalous signals, with intensities of nt on 21 (or 66) days, nt on 12 (or 57) days, nt on 3 (or 48) days, and nt on 1 (or 45) days prior to the first (or the second) earthquake. Using moving average procedure, we also see clear anomalous patterns reaching extreme magnitude of more than 200 nt during several days prior to the earthquakes. On these days, sigma Kp values were also extreme reaching abnormal values of more than 50 nt; but the background sigma Kp values were low. It means that some abnormalities were recorded globally, but we are not quite sure that whether geomagnetic storms occurred during the anomalous days. It is also possible that the anomalous signals were in close correlation to the earthquake occurrences, but they were not only locally detected over Indonesian region, moreover they spread globally due to the giant magnitude of the earthquake. Indeed the anomalies still persisted with approximately magnitude of 100 nt, then gradually decreased and until return to normal values in 112 days after the earthquake. Fig. 5. Three geomagnetic observatories and the location of studied earthquake in Indonesian region: LRM, KDU, and PHU with the giant M9.1 Sumatera Earthquake on December 26th 2004 and of another M7.5 one happened before on November 11th 2004.

6 Sigma Kp Daily mean of the total magnetic field differences (nt) Daily mean of the total magnetic field ( nt) TABLE IV. INTENSITY OF ANOMALOUS GEOMAGNETIC SIGNALS ON LRM, KDU, AND PHU PRIOR TO THE SUMATERA EARTHQUAKE Anomaly (nt) DOY 295 (21/66 days Earthquake on (DOY 316) and (DOY 361) DOY 304 DOY 313 (12/57 days (3/48 days DOY 315 (1/45 days LRM-KDU LRM-PHU KDU-PHU Sigma Kp IV. DISCUSSION Results of study show that big earthquakes generate some anomalous geomagnetic signals prior to the day of occurrences, which can be recorded by the nearby observatories. The highest anomalies mainly in the differentiation signals between two observatories, which one of them located closest to-, and another one located most distant from-, the epicenter. It is possibly because the closest observatory recorded the highest intensity, while the most distant recorded the lowest intensity, so that the differentiations are of greatest. However, in case of American region, TUC is the nearest to the epicenter and FRN is the farthest, therefore the differentiation signals of FRN-TUC should be the highest. Indeed those occurred more frequent in BOU-FRN signals, probably due to the location of FRN and TUC which are bounded to the epicenter by the same shoreline, while BOU is located on the high altitude (2682 m). Here BOU recorded much less signals than other two observatories. Anomalies in American region were less visible rather than ones in Japanese and Indonesian regions. We suggest that it was because larger distances between observatories to the epicenters, while the magnitude of earthquake is smaller. In contrast, the studied earthquake in Indonesian region is giant; therefore we observed anomalies even from rather remote observatories. The elevations of used observatories in Japanese and Indonesian regions are quite low, which one in Australia is only of 4 m above the sea level. We suggest further that observatories which are close to the sea level may more responsive to the earthquake. 53,400 LRM 53,200 53, ,600 KDU 46,400 46, ,900 PHU 44,700 44, (a) 7,100 Eq(2004/11/11) Eq(2004/12/26) M7.5 M9.1 LRM-KDU LRM-KDU 7 days running average 6,900 6, ,700 LRM-PHU LRM-PHU 7 days running average 8,500 8, ,700 KDU-PHU KDU-PHU 7 days running average 1,500 1, (b) Fig. 6. Geomagnetic anomalous signal related to the M9.1 giant Sumatera Earthquake on December 26th (a) The daily mean of the total geomagnetic fields observed by three observatories which are the closest to Indonesian region (LRM, KDU, and PHU), and (b) The differentiations signals of two observatories and the moving averages, with sigma Kp values of corresponding days to evaluate the global geomagnetic conditions.

7 All studied regions have tectonic setting with normal fault mechanisms, which is caused by subduction of oceanic crust into continental crust. However, in American region the subducting Cocos plate is only a very small with a relatively low subduction speed of 44 mm/year, in comparison with the giant subducting Indian oceanic plate with a speed of 75 mm/year. Further comparison to our previous study [15], we found that for other earthquakes with smaller magnitudes in Japanese region (on September 25 th 2003 and September 5 th 2004) anomalies were also clear. They were seen four to five times, from 99 days and 83 days prior to the earthquakes. These clear anomalies were generated due to closer distances from the epicentres to the observatories. It is quite regret that we have no data of some important dates from the studied observatories in America and Australia, which probably have been filtered out by the national institutions who supplied the data to the INTERMAGNET, because they were quite extreme while no reasonable high sigma Kp values on the days. On the other hand, it is possible that the extreme (filtered out) data are quite valuable for seismo-geomagnetic analysis. There were many of these data losses from LRM and KDU after November 11 th 2004 earthquake in Indonesia, therefore we could not analyze the most important days just before the giant Sumatera Earthquake on December 26 th It will be useful to compare the recent results with data from other nearby observatories, even more to use data from Indonesian observatories for comprehensive analysis. In this case, we also found that for this giant earthquake, the sigma Kp were quite extreme. We therefore need more studies of 27 days of solar cycle, whether or not the anomalous days were on the maxima cycles (as normal geomagnetic storms phenomena, otherwise seismogenic ones). We further suggest studying the Kp cycle within quite longer time interval, e.g years maybe enough. V. CONCLUSION We have processed geomagnetic signals and analyzed their correlations to three large magnitude earthquakes in Japanese, American, and Indonesian regions; and conclude that the geomagnetic signal processing is very valuable in searching appropriate precursors for successful earthquake predictions. Here we re-underline some important aspects: 1. Fast decreasing of geomagnetic intensities signals are showed prior to earthquakes in Japanese, American, and Indonesian regions. All observational results are back to the normal (base line) values after earthquake occurrences. 2. The highest anomalies mainly in the differentiation signals between two observatories, which one of them located closest to-, and another one located most distant from-, the epicentre. 3. The distances from the observatories to the epicentres and the magnitudes of earthquakes very affect the results, while observatories which are close to the sea level may more responsive to the earthquake. 4. The regional tectonic setting, including size and velocity rate of subductions, may also affect the results. 5. Some missing data (which probably have been filtered out by the national institutions who supplied the data to the INTERMAGNET) during earthquake days are in fact very valuable to complete the analysis. 6. Further studies which will be very useful for Indonesian region are: (i) comparing the recent results with data from other nearby observatories even more to get data from Indonesian observatories, and (ii) studies of 27 days of solar cycle in quite longer time interval (e.g years) to determine whether the extreme sigma Kp values prior to the giant earthquakes are seismogenic phenomena, otherwise normal geomagnetic storms ones. ACKNOWLEDGMENT This research is funded by the Indonesian Directorate of Higher Education under Hibah Penelitian Unggulan Perguruan Tinggi 2012 program entitled Pengolahan Sinyal Seismo- Geomagnetik untuk Mitigasi Bencana Gempa Bumi Tektonik Regional di Wilayah Indonesia Timur (Seismo-Geomagnetic Signals Processing for Regional Tectonic Earthquake Hazard Mitigations of Eastern Indonesian Regions). The results presented in this paper rely on data collected at magnetic observatories. 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