بررسي زمان وقوع زلزله به كمك تحليل زمان طبيعي براي زلزله‌ي 5/5 ريشتري جمهوري آذربايجان

Investigation of the time occurrence of Azerbaijan earthquake M=5.5 by natural time analysis

زلزله به عنوان يكي از بلاياي طبيعي، از نظر جاني و مالي همواره خطري براي جوامع بشري محسوب مي شود؛ به همين دليل، تلاش براي پيش بيني زلزله به عنوان يكي از راه كارهاي مقابله با زلزله همواره مورد توجه بوده است. از طرفي كشور ايران با قرارگيري در كمربند كوهزايي آلپ- هيماليا كه يكي از لرزه خيزترين مناطق جهان است، از نظر لرزه خيزي در وضعيت لرزه خيزي شديد قرار دارد. يكي از موفق ترين پيش نشانگرهاي كوتاه-مدت زلزله، سيگنال هاي الكتريكي لرزه اي (SES) است كه روش VAN ناميده شده است. در اين ارتباط از اوايل سال 1393 ايستگاه هايي جهت ثبت و پايش سيگنال هاي الكتريكي لرزه اي در شمال غرب ايران نصب گرديده است. با دريافت و تحليل اين سيگنال ها، مي توان بزرگا، رومركز و زمان زلزله ي قريب الوقوع را تعيين كرد. اين پژوهش به بررسي SES دريافت شده در تاريخ 16 مرداد 1394 و چگونگي انجام تحليل هاي زمان طبيعي جهت پي بردن به زمان وقوع زلزله ي پيش رو در بازه ي زماني كمتر از يك هفته مي پردازد. نتايج تحليل هاي زمان طبيعي نشان داد كه اين سامانه در تاريخ 12 شهريور 1394 به مرحله ي بحراني رسيده است و متعاقبا در صبح 13 شهريور 1394 زلزله ي اصلي اين سامانه به بزرگاي 5/5 ريشتر در منطقه ي ايقوز جمهوري آذربايجان و در فاصله ي 310 كيلومتري از ايستگاه اسپيران به وقوع پيوست. نكته ي مهم در اين رابطه اين است كه در فاصله ي زماني 6 ماه پيش و 6 ماه پس از اين زلزله، هيچ زلزله ي بزرگتر از 5 ريشتري در منطقه مورد مطالعه رخ نداده است؛ كه خود تاييدي بر اتفاقي نبودن اين پيش بيني است.

IntroductionEarthquakes as natural disasters, are always considered to be a risk for human societies in terms of economy and life. Therefore, attempts to predict earthquakes have always been considered as a way of risk management. On the other hand, Iran is located in a critical seismic condition through the Alpine-Himalayan orogenic belt, which is one of the most seismic areas in the world. Talesh Mountains are located in North West of Iran, in the south of the Caucasus orogeny, east of the Anatoly, and north of the Zagros orogeny. Many minor and major earthquake faults such as Tabriz fault, North Anatoli fault, East Anatoli fault, Zagros main fault and Alborz Western faults are effective in this area.Materials and methodsEarthquake prediction by electric precursors, known as VAN method, is one of the most successful short-term methods of earthquake prediction. This method (VAN) is based on researching the changes in Geo-electric potentials, called seismic-electric signals (SES) which can be detected before earthquakes. SES could be shown in special locations (sensitive sites) and sensitive sites receive the SES as a selection from the seismic sources. Therefore, it is possible to estimate the location of the event up to 100 Kms far away. The magnitude of the progressive earthquake could be forecasted up to 0.7-unit tolerance in Richter scale. Professor Vrotsos that is the founder of the VAN method and director of the solid state physics in University of Athens has published more than 250 papers and 8 books in this subject. In the last two decades the VAN team developed the time series analysis to forecast earthquakes, called “Natural time analysis”. In this paper, according to this method, the occurrence of one earthquake M=5.5 is analyzed. Results and discussionSince 2014 a network of VAN stations were installed in NW Iran for recording and monitoring the Seismic Electric Signals (SES). Receiving and analyzing these signals, could help determine the magnitude, epicenter and time of impending earthquakes. This research investigates an SES received on 7th of August 2015 and application of natural time analysis to find out the time occurrence of the subsequent impending earthquake, in a time window less than a week. The natural time analysis indicates that this system reached the critical point, on September 3rd 2015 and subsequently on 4th of September 2015 the 5.5 Richter (MN) main shock occurred in Oghuz municipality in the Republic of Azerbaijan, at a distance of 310 km from Ispiran station. The important point is that this earthquake is the only earthquake greater than 5 Richter occurring in the study area in 6 months before and after this event. This confirms that this prediction wasn’t random.ConclusionSince 2014 a network of VAN stations were installed in NW Iran for recording and monitoring the Seismic Electric Signals (SES). Receiving and analyzing one of the signals, helped determine the magnitude, epicenter and time of impending earthquakes. This research investigates an SES received on 7 August 2015 and how to apply the natural time analysis to find out the occurrence of the subsequent impending earthquake, in a time window less than a week. The natural time analysis indicates that this system reached the critical point, on 3 September 2015 and subsequently On 4 September 2015 the 5.5 Richter (MN) main shock occurred in Oghuz municipality in the Republic of Azerbaijan, at a distance of 310 km from Ispiran station.