The point source parameters of the April 12, 2012 Mw 7.0 Santa Isabel, Mexico, earthquake indicated by teleseismic P and SH waveforms obtained by a means of traditional cut and paste（CAP） method show that the best double-couple solution of this event is： 37°/127°, 90°/81° and-9°/-180° for strike, dip and rake, respectively. Its centroid depth is 13 km. Global teleseismic waveform data exhibit that the rupture of the earthquake initiated at a focal depth of 13 km and propagated southeastward with a relatively slow rupture velocity（about 1.8 km/s on average）. The maximum slip occurred at 30 km southeast of the hypocenter, with the peak slip of 3.57 m and total seismic moment of whole fault up to 3.98×1019 N·m. These observations provide some insight into properties, co- or post-seismic deformation and coulomb stress changes of future earthquake in this area.
Co-seismic deformation and gravity field changes caused by the 2011 Mw6. 8 Myanmar and Mw6. 9 India-Nepal earthquakes are calculated with a finite-element model and an average-slip model, respectively, based on the multi-layered elastic half-space dislocation theory. The calculated maximum horizontal displace- ment of the Myanmar earthquake is 36 era, which is larger than the value of 9. 5 cm for the India-Nepal earth- quake. This difference is attributed to their different focal depths and our use of different models. Except cer- tain differences in the near field, both models give similar deformation and gravity results for the Myanmar event.
Earthquake magnitude and rupture duration are among the most important parameters characterizing an earthquake for the purpose of early tsunami warning. While they can be routinely determined from broadband P waveforms with iterative inver- sion procedures, the inversion procedures may fail when the rupture either lasts longer than the interval between P and later ar- rivals or requires too much time or human intervention. Little contaminated by later arrivals, high frequency P waves are useful for modeling earthquake source processes, though the envelope waveform is affected by strong scattering in lithosphere. With high frequency envelopes from aftershocks as Empirical Green＇s Function （EGF）, the coda effects can be removed and more accurate relative source time function （RSTF） of the main shock can be obtained. Assuming that RSTFs cannot be negative, we use the projected Landweber deconvolution method （PLD） to obtain high frequency RSTFs because PLD method has the ad- vantage of non-negativity, causality, and compactness （finite duration）. We are able to determine rupture durations of four large earthquakes： the 2004 Sumatra-Andaman earthquake, the 2005 Nias event, the 2006 Java event, and the 2011 Tokuko earthquake. The rupture durations of the Sumatra-Andaman, Nias, and Tohuko events are found to be around 550, 1 i0, and 120 s respectively, consistent with previous studies. The rupture duration of the Java event is about 130 s, supporting that the Java event is a tsunami earthquake. The magnitudes of these earthquakes are found to depend on both the amplitude and the duration of the deconvolved waveforms, and can be approximated by integrating these waveforms.
Based on teleseismic data obtained from 225 stations from two networks in the central Tibetan plateau, we have generated detailed crustal structure images using P-wave receiver function techniques with more accurate piercing-depth-correction and time-depth-correction than what have previously been available. Our images indicate an undulatory Moho beneath the Tibetan plateau with a steep jump beneath the northern Himalaya, and obviously different structures in proximity to the Bangong-Nujiang suture. In several sections of the Tibetan plateau, the lower crust is characterized by pervasive high-velocity regions, which are consistent with the preservation of eclogite bodies beneath the plateau, whose presence affects the dynamics of the Tibetan plateau.
Can GeYoushun SunM Nafi TokszYingcai ZhengYong ZhengXiong XiongDiming Yu
北京时间2013年4月20日,四川省雅安市芦山县发生了Ms7.0级大地震,造成了惨重的人员伤亡和经济损失.基于四川省及周边省市区域台网近震波形数据以及IRIS远震波形数据,利用CAP(Cut And Paste)方法及其发展方法分别对近震、远震数据进行单独反演以及联合反演,得到各自的震源机制解和震源深度.结果显示,不同方法得到的震源机制解和震源深度都比较稳定,其中联合反演得到的最佳震源机制解为:节面Ⅰ走向210°,倾角44°,滑动角91°;节面Ⅱ走向29°,倾角46°,滑动角89°;震源深度为16km,震级为Mw6.66.为了验证结果的可靠性,基于不同模型对近震数据进行反演测试,发现在龙门山地区,复杂的速度结构对反演震源机制解有10°左右的影响,对震源深度的影响有2km左右.另外,对远震数据,按震中距进行重采样,所得结果非常一致,说明远震数据对芦山地震震源信息约束比较稳定.
