بررسی فعالیت گسل درونه براساس سازوکار کانونی زمینلرزه های دو دهه اخیر

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشگاه فردوسی مشهد

2 پژوهشگاه بین الملللی زلزله شناسی و مهندسی زلزله

3 صندوق حمایت از پژوهشگران کشور

4 پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله

چکیده

چکیده

بررسی های فعالیت گسل ها مهمترین ابزار برای تعیین جهت‌گیری میدان تنش هستند.با محاسبه سازوکار کانونی زمین لرزه ها جهت انتشار گسیختگی، هندسه گسل و میدان تنش منطقه مورد مطالعه را می توان مشخص نمود. گسل درونه با طول حدود 800 کیلومتر بعد از گسل اصلی زاگرس بزرگترین گسل ایران است. هدف از این پژوهش مطالعه لرزه‌خیزی، حل سازوکار کانونی زمین‌لرزه‌های رخ داده در راستای سه بخش غربی، میانی و شرقی گسل درونه و تخمین تنش در منطقه است. در این مطالعه محاسبه سازوکار کانونی با استفاده از روش پلاریته (قطبش) اولین رسید موج P برای 21 زمینلرزه بزرگتر از 3 رخ داده در مجاورت گسل درونه طی دو دهه اخیر انجام می شود. علاوه بر آن برای راستی آزمائی نتایج از مدل سازی شکل موج برای محاسبه سازوکار کانونی زمینلرزه های کمتر از 4 استفاده می شود. سپس از بررسی سازوکارهای محاسبه شده، مقادیر تنش آزادشده در صفحه‌های گسلی ارائه می‌گردد.سازوکارکانونی رویدادها و مقایسه آن با بررسیهای زمینساختی پیشین در راستای گسل درونه همخوانی قابل قبولی دارد. نتایج مطالعه حاضر نشان می‌دهد تفاوت قابل ملاحظه ای در سازوکار کانونی زمین‌لرزه‌های سه قطعه شرقی، میانی و غربی گسل درونه وجود دارد که تائیدکننده حرکت بلوک‌ها به دوصورت چپ‌بُر و راست‌بُردر راستای گسل است.اختلاف سازوکارکانونی رویدادهای بخش‌های شرقی و غربی با توجه به حرکت رو به شمال بلوک لوت و انحنای گسل درونه توجیه پذیر است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Investigation of the Dorouneh fault system based on the focal mechanism of the earthquakes of the last two decades

نویسندگان [English]

  • Mohadeseh Asar Enayati 1
  • Gholam Javan Doloei 2
  • Somayeh Ahmadzadeh 3
  • Azar Afshar Savat 4
1 Ferdowsi University of Mashhad
2 International Institute of Earthquake Engineering and Seismology
3 INSF-Iran
4 International Institute of Earthquake Engineering and Seismology
چکیده [English]

Fault plane solution is one of the most important tools to determine the orientation of the stress field. The focal mechanism of earthquakes can be applied to determine the direction of rupture propagation, the structure of the fault and the stress field of the region. Dorouneh fault is the largest fault in Iran after the main Zagros fault with about 800 km length. The purpose of this study is to investigate the seismicity the stress field and the focal mechanism of earthquakes that have occurred across the three main segments western, middle and eastern parts of the Dorouneh fault. Therefore, the calculation of the focal mechanism is performed using the P-wave first-motion polarity. Also the stress situation of the events and the recognition of fault planes are presented in this research. Along this fault, the blocks have moved in both left and right directions, but certainly one of its last movements has right lateral motion. In this study, the waveforms recorded at the seismic stations of the National Seismological Center of Tehran University (IRSC), the National Center of Broadband Seismic Network of Iran belong to the International Institute of Earthquake Engineering and Seismology (IIEES) and seismic stations of Seismological Research Center at the Ferdowsi University of Mashhad was used. At the first, the waveforms of each seismic event were combined with each other, and then the relocation of the events were determined based on new data set of this study (Figure 2). A number of high quality earthquake with a magnitude of more than 3 and an average depth of 14 km have been selected (which their list is presented in table 1) to calculate fault plane solution.

In order to calculate the mechanism of the recent earthquakes in the Khorasan region, interesting results have been obtained based on several methods (Assar Enayati, 1400). One of the common methods for estimating the mechanism of earthquakes, especially earthquakes with small magnitudes and at close distances from the epicenter, is the polarization of the first arrival of the P wave. Due to the dependence of the amplitude and polarization of the P wave on the focal mechanism, by determining the polarization of the first arrival of the seismic phase, the earthquake focal mechanism can be calculated. The results of focal mechanism solutions for significant events around Dorouneh fault show mostly left lateral strike slip motion which is consistent with the tectonic setting of the region.The difference in the focal mechanism of the events in the eastern and western parts of the fault is justified by the northward movement of the Lut block. The integration of data shows high accuracy in calculating the mechanism and more certainty about the results. Therefore, in the direction of the Dorouneh fault, the movements are both left-handed and right-handed from the seismic situation. The change in the mechanism obtained from the seismic results, considering that the stress axes show changes, can represent the second and third order stress fields that balance the stress in this area today. The second-order stress can be related to continental rifting, isostasy adaptation, topography and de-glaciation, and the third-order stress field can be related to the local stress source on a scale smaller than 100 km, which is influenced by the structural geometry, and interference between fault systems, topography and local density difference (Sheikh-ul-Islami et al., 2021).

کلیدواژه‌ها [English]

  • focal mechanism
  • wave polarization
  • seismicity
  • Dorouneh fault
  • state of stress