تحلیل و روندیابی پارامترهای مبنایی پیش لرزه‌ها و پس‌لرزه‌های زمین‌لرزه آذرماه 1391 زهان در استان خراسان‌جنوبی

تحلیل زمان، مکان و بزرگی پیش‌لرزه‌ها و پس لرزه‌ها از جمله مواردی است که در دهه‌های اخیر مورد توجه متخصصان رشته‌های مرتبط از جمله زمین‌لرزه‌شناسان، مهندسان سازه، مدیران بحران و دیگر علوم مرتبط قرار گرفته است. زیرا این تحلیل‌ها در کنار شناسایی شرایط لرزه‌زمین‌ساختی منطقه و رفتار گسل مسبب زمین لرزه، کمک زیادی به روندیابی پیش‌لرزه‌ها و پس‌لرزه‌ها با هدف کاهش تلفات و حتی کاستن تنش‌های روانی جامعه آسیب دیده و بازمانده در منطقه زلزله‌زده و مدیریت کارآمد بحران در آن شرایط می‌کند. در این مقاله به بررسی و ارزیابی داده‌های مربوط به یک زمین‌لرزه واقعی و تجربه مشابه به‌دست آمده از دیگر زمین‌لرزه‌ها و ارائۀ الگویی کاربردی در زمینۀ پیش‌بینی پارامترهای زمین‌لرزه اصلی و هم‌چنین مکان‌یابی و تعیین بزرگی و زمان پس‌لرزه‌ها با هدف کاهش اثرات ناشی از آنها در مناطق زلزله‌زده می‌پردازیم. بر این اساس، در پژوهش حاضر، نتایج بررسی‌های مربوط به تحلیل مبنایی پارامترهای پیش‌لرزه‌ها و پس‌لرزه‌های زمین‌لرزه آذرماه 1391 زهان در استان خراسان جنوبی بررسی شد. اهمیت بررسی و پژوهش‌های کاربردی در این بخش از ایران به دلیل این است که این بخش از ایران با این‌که در دهه‌های گذشته شاهد زمین‌لرزه‌های مخرب و بزرگی بوده است، در بیش از دو دهۀ اخیر، با یک نبود لرزه‌ای مشخص مواجه شده است. چنین شرایطی، بررسی متمرکزتر در بارۀ تغییرات لرزه‌خیزی در این محدوده، به‌دلیل قریب‌الوقوع بودن یک زمین لرزه بزرگ را ضرورت می‌بخشد. نتایج به‌دست آمده از این پژوهش روی تحلیل روند تغییرات پیش‌لرزه‌ها نشان داد که با بررسی تغییرات مکانی،‌ بزرگی و عمق پیش‌لرزه‌ها می‌توان تا حدود زیادی به روند یابی پارامترهای زمین‌لرزه‌ اصلی رسید. ضمن این‌که فراوانی پس لرزه ها و فواصل زمانی(سکون لرزه ای) مشخص بین آنها می‌تواند به‌عنوان نشان‌گرهایی برای شناسایی زمان پس لرزه های بزرگ‌تر استفاده شود و تحلیل‌های انجام شده در این پژوهش نشان داد روش‌هایی از جمله مدل‌های ارائه شده در بارۀ سری زمانی در کنار تحلیل سکون لرزه‌ای به تدقیق زمان پیش‌بینی پس‌لرزه‌های بزرگ می‌انجامد.

Analysis and routing of basic parameters of foreshocks and aftershocks in Zohan earthquake, 2012 in south khorasan

Introduction Analysis of time, location and magnitude of foreshocks and aftershocks has been one of the most important cases for experts in various scientific fields such as: seismology, structural engineering and crisis management, and other interrelated fields. Since this analysis and the result of studies on seismotectonic and cases of earthquakes help us identify the foreshocks and aftershocks with the goal of decreasing losses and nervious stress of the injured community in quakestricken areas and skilled crisis management. The cause fault of earthquake plays the important role in foreshocks and aftershocks of the earthquake. So, study on fault behaviour is a suitable method for analyzing and routing the basic parameters of foreshocks and aftershocks. Also, foreshocks and aftershock are important parts of any earthquake in a seismic area. The analysis of the basic parameters of the foreshocks is one of the most practical researches for reducing the risk of earthquakes. The identification of behavioral pattern of foreshocks can help researchers detect the active fault conditions for the occurrence of earthquakes in different areas. The present study is concerned with the study of behavioral patterns earthquakes, foreshocks, and aftershock of Zohan earthquake. Experience of large aftershocks in different parts of the world indicates that, following earthquakes and depending on seismictectonic conditions, large aftershocks are likely to occur in the earthquakeeffected zone, which will aggravate the damage caused by earthquakes (Omi et al., 2013). The main factor contributing to the worsening of damage caused by aftershocks is the performance of structures that are weakened but not destroyed by main earthquakes and are, thus, highly likely to be destroyed by large aftershocks (Saket and Fatemi Aghda, 2006).Material and methodsThe present paper makes use of data collected in a real earthquake and similar expriences in other earthquakes for presenting a practical pattern for predicting primary earthquake patterns, determining the location, magnitude, and time of aftershocks. The target of this case is decreasing the effects of earthquake. To this end, we used the results from studies on basic parameters of foreshocks and aftershocks of Zohan earthquake, and 2012 earthquake in South Khorasan province. The rationale for selecting the aforementioned studies is: location of event, the Zohan earthquake, had been identificated as an area with high risk for the occurrence of earthquakes, although there has been no widescale earthquake in this area in the last two decades. These conditions are important causes for more concentrated studies on this area because there is a high chance for widescale earthquakes striking this area.Result and DiscussionIn this part of research, we conduct a study on the location, magnitude and depth of foeshocks. Some of the worldwide research suggested that these data can help to predict the time of mainshocks. Studies conducted on the variations of frequency in foreshocks can follow this goal.In this paper, the available statistical data such as periodical variations of seismicity in the weeks leading up to the main shock can be used as a tool for estimating the approximate time of a future important earthquake. The weekly variations of seismicity before Zohan earthquake indicate a relative increase and then decrease within a 100 km radius around the epicenter of the main shock. Table 1: Variations of frequency of foreshock based magnitude before Zohan earthquakeWeek before main shockFrequency of foreshock in the Radius of 100Km from main shockFrequency of foreshock(with M>2.5) in the Radius of 100Km from main shock600511410320253120 Studies on numerous earthquakes in Iran and other regions in the world show that the distribution of aftershocks can be related to fault type or the direction of principal stress (Saket and Fatemi Aghda, 2006) and (King et al., 1994). Whereas maximum Coulomb stress change is related to maximum principal stress in earthquakes, the concentration of aftershocks can coincide with the direction of maximum principal stress ( sigma;1) of the causative fault in mainshock. Considering the direction of maximum principal stress and its adaptation to the scattering of aftershocks, the above hypothesis is confirmed.Also studies on frequency changes and seismic quiescence of small aftershocks help us in predicting future aftershocks. The results the of presented research by Itawa (2008) on the World earthquake catalogue suggest that seismic quiescence theory is true for different regions of the world. Based on the results of the study mentioned above, this case can be used as a tool for predicting large aftershocks in Zohan earthquake.Fig 1. Adaptation of direction of maximum principal stress with scatering of the aftershocks of Zohan earthquake. a: direction of maximum principal stress ( sigma;1) of the causative fault in mainshock. b scaterring of the aftershocksTable 2: Seismic sequience versus magnitude of aftershocksRowSeismic Quiescence for aftershocksAftershock MagnitudeData and Time of aftershocks1133.02012/12/0517:21:032363.42012/12/0517:57:0331613.12012/12/0520:38:09439063.92012/12/0813:44:19In addation, frequency of aftershocks and certain time distance (seismic quiescence) between their can use precursors for detecting the time of large aftershocks. The relevant analysis in this study showed that methods such as: time series beside seismic quiescence can help in conducting a more accurate time forecast of large aftershocks.ConclusionThe results of this research suggest that we can identify some of the charactristics of the main shock by focusing on location, magnitude and depth of foeshocks.In Zohan earthquake, the direction of maximum principal stress is adpated to the scattering of aftershocks, and this case suggests that there is a specific relationship between them.The relevant analysis in this study showed that the methods such as: time series beside seismic quiescence can help conduct a more accurate time forecast of large aftershocks../files/site1/files/144/saket.pdf