بررسي ارتباط بين تغييرات استرس كولمب و توزيع مكاني پس لرزه‌ها : به منظور برآورد عمق زمين لرزه‌ها در كمربند زاگرس

Investigation of Correlation between Coulomb Stress Changes and Aftershock Spatial Distribution: to Estimate Depths of Earthquakes in the Zagros Belt

يكي از گسترده‌ترين معيارها براي مطالعه نواحي تغيير تنش حاصل از رخداد يك زمين‌لرزه، معيار كلمب است. عمق زمين‌لرزه‌هاي زاگرس همواره مورد سؤال بوده است. در اين پژوهش اين مدل براي سه زمين‌لرزه نسبتاً بزرگ زاگرس بكار گرفته شده است. اين زمين‌لرزه‌ها عبارتند از: زمين‌لرزه 27 مرداد 1393 ايلام (با بزرگي گشتاوري 6/2)، 20 فروردين 1392 بوشهر (با بزرگي گشتاوري 6/3) و 20 شهريور 1387 قشم (با بزرگي گشتاوري 6/1). در اين زمين‌لرزه‌ها انطباق بين توزيع مكاني پس‌لرزه‌ها و محيط‌هاي افزايش تنش حاصل از رخداد شوك اصلي در اعماق مختلف با هم مقايسه شدند. نتيجه كار نشان مي‌دهد كه عمق 5 كيلومتر براي زمين‌لرزه‌هاي ايلام و بوشهر و عمق 5/5 كيلومتر براي زمين‌لرزه‌ي قشم منطقي به نظر مي‌رسد. در اين پژوهش يكي از كاربردهاي استفاده از تغييرات تنش كلمب حاصل از رخداد يك زمين‌لرزه جهت محاسبه پارامترهاي زمين‌لرزه معرفي گردد.

The Coulomb failure stress (CFF), most distributed criteria describes static stress changes in nearby areas of an earthquake. Many researches have been done to verify that there is a great correlation between stress increase areas of an earthquake and its aftershocks spatial distribution or later events location. We employed this fact to identify earthquake depths of latest Zagros larger events. The exact depth of Zagros earthquakes are ambiguous and other techniques used to calculate the depth of a teleseismic earthquake. Sometimes different amounts reported from different CMT centers. Aftershocks are recorded by local Seismic Stations, are more exact. We use the correlation between stress increase areas of an event and spatial distributions of its aftershocks to calculate most exact of that event. This study done for three large events: the Ilam earthquake, 18 August 2014 (MW=6.2); the Boushehr earthquake. 9April 2013 (MW=6.3) and the Qeshm Earthquake, 10 September 2008 (MW=6.1). The correlation between stress increase areas of each of them and their aftershocks spatial distribution are checked in different depths, reported by CMT centers and average zagros sedimentary rocks (average depth of medium to large earthquakes of Zagros). The results show that when the depth is equal to average Zagros carbonated sedimentary cover (brittle bed), the best correlation between stress increase areas of an event and its spatial distribution of aftershocks can be seen. So we considered 5 Km depth for Ilam and Boushehr, and 5.5 Km for Qeshm earthquakes. The previous studies also confirm our results. So here it is introduced one of multiple applies of the coulomb static stress change calculations