كليدواژه :
روش‌هاي سينماتيكي , مدل‌سازي گسل و مدل موانع ويژه , زلزله لاكوئيلا , طيف چشمه زلزله , شبيه‌سازي زلزله لاكوئيلا ايتاليا 2009
چكيده فارسي :
هم زمان با پيشرفت نياز جوامع به سازه هاي پيچيده تر، نياز به شناخت بيشتر بارهاي وارده برسازه به ويژه بارهاي لرزه اي نيز گسترش مي يابد. داشتن تخميني قابل اطمينان از حركات قوي زمين در يك ساختگاه مشخص، بدون داشتن شناخت صحيح از مكانيزم توليد امواج لرزه اي، عوامل ساختاري اثرگذار بر اين امواج در مسير انتشار، و شناخت شرايط فيزيكي محل ساخته شدن سازه ها ميسر نخواهد بود. در اين ميان، مدل موانع ويژه كه از مشهورترين روش هاي سينماتيكي شبيه سازي گسل زلزله مي باشد، گسل را به عنوان مجموعه از ترك هاي دايره اي در نظر مي گيرد. گسيختگي به صورت افت تنش هاي موضعي در اين ترك ها فرض مي شود، و توقف و شروع هاي مكرر گسيختگي، عامل اصلي توليد امواج فركانس بالا در اين مدل است. در اين مطالعه سعي شده است با استفاده از مدل موانع ويژه به شبيه سازي چشمه گسل مولد زلزله لاكوئيلا در كشور ايتاليا اقدام شود، همچنين در سوي ديگر با استفاده از روابط كاهندگي مناسب منطقه تاثيرات مسير انتشار امواج در مدل سازي لحاظ شود. در انتها نيز به كمك ضرب توابع انتقال لايه هاي سطحي خاك تاثيرات ساختگاه بر نتايج اعمال گشته و نتايج را قابل مقايسه با نتايج به دست آمده از زلزله مذكور ساخته است.
چكيده لاتين :
Earthquakes are one of the most Terrible danger that are likely to cause heavy human losses and destroy entire civilization on scale of minutes. The more recent damaging events in Mexico City (1985 Mexico) in bam (2003 Iran) or Tohoku (2011 Japan) recall that so far little is known about earthquake physics that could prevent people from their deadly effects. To reduce casualties Decades of research involving numerous laboratories worldwide aim at investigating this large scale phenomenon and trying to understand how it triggers, propagates, and stops. A trusty physical modeling of strong ground motion requires to examine three crucial parameters of seismic source specifications, wave propagation path, and seismic site effects. A reliable physical modeling of strong ground motion requires to examine three crucial parameters of seismic source specifications, wave propagation path, and seismic site effects. Among various seismic source specifications, a more physically realistic source model is the specific barrier model or (SBM) for short. The SBM is specifically more suitable for regions with poor seismological data bank and/or ground motions from large earthquakes with large recurrence intervals. In order to simulate seismic ground motions from a specific earthquake source model in an efficient way, the stochastic modeling method has been widely used. An essential part of the seismological model used in this method is the quantitative description of the far-field spectrum of seismic waves emitted from the seismic source. Since shear (S) wave is primarily the main factor of earthquake damages, the application of stochastic approach of the SBM has almost been focused on the far-field S wave spectrum, in which two corner frequencies of observed earthquake are represented. The ‘two-corner-frequency’ shows two considerable length-scales of an earthquake source: a length-scale that quantifies the overall size of the fault that ruptures (e.g., the length L of a strike-slip fault) and another length-scale that measures the size of the subevents. Associated with these length-scales are two corresponding time scales: (1) the overall duration of rupture, and (2) the rise time. The SBM has a few main source parameters which have been calibrated to earthquakes of different tectonic regions. In this paper, it has been tried to simulate source, path and site of entire earthquake and compare the results of simulation with real earthquake. To this end SBM with uniform PDF for arrival time but different types of PDFs of subevent size used to simulate source. To investigate effect of PDFs of subevent size on the source spectra as well as earthquake spectra as result of simulation, uniform and fractal distribution along with classic distribution for subevent size are considered. In order to take into account, the effects of path of propagation, Geometric and inelastic Attenuation Compatible with center of Italy (L’Aquila region) have been used. Finally, to considering effect of the layers of soil (sediments) near surface on amplitude, period, duration and other characteristic of seismic waves, transfer function for linear wave propagation has been computed with the Thomson-Haskell matrix method. Transfer function in this method illustrate how a soil column with different layers attenuates and amplifies seismic waves as a function of frequency.
