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91.
2013年芦山M_S7.0地震产生的静态库仑应力变化及其对余震空间分布的影响 总被引:5,自引:0,他引:5
2013年4月20日芦山MS7.0地震发生在龙门山断裂带的西南段,距2008年汶川MS8.0地震仅约85km,时间上仅相隔5年.首先计算了汶川地震的静态库仑应力变化对本次芦山地震的影响,得出芦山地震是由汶川地震触发造成的(库仑应力上升了0.012 MPa);进一步计算了芦山地震与汶川地震这两次大地震共同产生的静态库仑应力变化.结果表明,芦山地震的余震受前面两次大地震的共同影响,而不仅仅是芦山地震单独作用的结果,超过85%的余震发生在两次地震共同产生的静态库仑应力变化增大的地方,而芦山地震本身触发不了本次的余震序列(仅48.7%的余震位于主震所产生的应力加载区).此外,计算结果表明芦山地震本身对周边断层影响较小,仅龙门山断裂带的东北段受到一定的加载作用;而由于汶川地震的作用,安宁河断裂、大凉山断裂、马尔康断裂、岷江断裂和虎牙断裂呈卸载趋势,仅鲜水河断裂东南段和龙门山断裂中段受到加载作用,这均会加速断层上新地震的发生. 相似文献
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根据地震破裂过程中的多普勒效应,利用多台波谱参数推算九江-瑞昌Ms5.7地震的震源破裂参数,得到主震的破裂方位角ψ0≈319.6°,破裂速度约为2.3 km/s,用最小二乘法拟合的相关系数极值约为0.80.在此基础上,分别计算了主震在4.8级强余震的两个节面上的静态库仑应力变化量,结果显示:主震在4.8级余震节面Ⅰ、Ⅱ上的静态库仑应力变化均为正值,分别为0.48 MPa和0.02 MPa.主震在节面Ⅰ、Ⅱ上产生的静态库仑应力的变化十分接近.应力增加的区域主要位于主震断层的右侧,应力减小的区域主要分布在震中南部.统计显示:绝大部分余震均发生在静态库仑应力增加的区域内,尤其是在节面Ⅰ上,表明主震破裂产生的库仑破裂应力变化对4.8级余震的发生有重要的触发作用,同时也有利于大多数余震的发生. 相似文献
94.
S.?SantiniEmail author P.?Baldi M.?Dragoni A.?Piombo S.?Salvi G.?Spada S.?Stramondo 《Pure and Applied Geophysics》2004,161(4):817-838
— The study of surface deformation due to seismic activity is often made using dislocations with uniform slip and simple geometries. A better modeling of coseismic and postseismic surface displacements can be obtained by using dislocations with variable slip and nonregular shapes. This is consistent with the asperity model of fault surfaces, assuming a friction distribution on faults made of locked zones with much higher friction than surrounding zones. In this paper we consider the 1997–1998 Colfiorito seismic sequence. The coseismic surface displacements in the Colfiorito zone are used in order to infer the slip distribution on the fault surface at different stages of the sequence. The displacement field has been modeled varying the slip distribution on the fault, and comparing the deformation observed by SAR and GPS techniques with model results. The slip distribution is calculated by Monte Carlo simulations on a normal fault with the dip angle equal to 40°. A good approximation is obtained by using square asperity units of 1.5×1.5 km2. In the first stage, we employed a simplified model with uniform slip, in which each asperity unit is allowed to slip a constant amount or not to slip at all, and in the second stage, we evaluate the slip distribution in the dislocation area determined by the Monte Carlo inversion: in this case we allow unit cells to undergo different values of slip in order to refine the initial dislocation model. The results show that the 1997 seismic events of the sequence can be modeled by irregular dislocations, obtaining a good fit to the DInSAR and GPS observations. The model also confirms the results of previous studies by a different methodology, defining the distribution of asperities on the fault plane using the fault geometry, the geodetic data and the seismic moment of the 1997–1998 Colfiorito seismic sequence. Furthermore, the analysis of 1997 aftershocks in the seismogenic region shows a strong correlation between most events and the asperity distribution, which can be considered as an independent test of the validity of the model. 相似文献
95.
Lapo Boschi 《Geophysical Journal International》2006,167(1):238-252
I invert a large set of teleseismic phase-anomaly observations, to derive tomographic maps of fundamental-mode surface wave phase velocity, first via ray theory, then accounting for finite-frequency effects through scattering theory, in the far-field approximation and neglecting mode coupling. I make use of a multiple-resolution pixel parametrization which, in the assumption of sufficient data coverage, should be adequate to represent strongly oscillatory Fréchet kernels. The parametrization is finer over North America, a region particularly well covered by the data. For each surface-wave mode where phase-anomaly observations are available, I derive a wide spectrum of plausible, differently damped solutions; I then conduct a trade-off analysis, and select as optimal solution model the one associated with the point of maximum curvature on the trade-off curve. I repeat this exercise in both theoretical frameworks, to find that selected scattering and ray theoretical phase-velocity maps are coincident in pattern, and differ only slightly in amplitude. 相似文献
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97.
Prantik Mandal R. Narsaiah B. Sairam C. Satyamurty I. P. Raju 《Pure and Applied Geophysics》2006,163(8):1561-1581
We employed layered model joint hypocentral determination (JHD) with station corrections to improve location identification
for the 26 January, 2001 Mw 7.7 Bhuj early and late aftershock sequence. We relocated 999 early aftershocks using the data from a close combined network
(National Geophysical Research Institute, India and Center for Earthquake Research Institute, USA) of 8–18 digital seismographs
during 12–28 February, 2001. Additionally, 350 late aftershocks were also relocated using the data from 4–10 digital seismographs/accelerographs
during August 2002 to December 2004. These precisely relocated aftershocks (error in the epicentral location<30 meter, error
in the focal depth estimation < 50 meter) delineate an east-west trending blind thrust (North Wagad Fault, NWF) dipping (~
45°) southward, about 25 km north of Kachchh main land fault (KMF), as the causative fault for the 2001 Bhuj earthquake. The
aftershock zone is confined to a 60-km long and 40-km wide region lying between the KMF to the south and NWF to the north,
extending from 2 to 45 km depth. Estimated focal depths suggest that the aftershock zone became deeper with the passage of
time. The P- and S-wave station corrections determined from the JHD technique indicate that the larger values (both +ve and
-ve) characterize the central aftershock zone, which is surrounded by the zones of smaller values. The station corrections
vary from −0.9 to +1.1 sec for the P waves and from −0.7 to +1.4 sec for the S waves. The b-value and p-value of the whole
aftershock (2001–2004) sequences of Mw ≥ 3 are estimated to be 0.77 ± 0.02 and 0.99 ± 0.02, respectively. The p-value indicates a smaller value than the global
median of 1.1, suggesting a relatively slow decay of aftershocks, whereas, the relatively lower b-value (less than the average
b-value of 1.0 for stable continental region earthquakes of India) suggests a relatively higher probability for larger earthquakes
in Kachchh in comparison to other stable continental regions of the Indian Peninsula. Further, based on the b-value, mainshock
magnitude and maximum aftershock magnitude, the Bhuj aftershock sequence is categorized as the Mogi's type II sequence, indicating
the region to be of intermediate level of stresses and heterogeneous rocks. It is inferred that the decrease in p-value and
increase in aftershock zone, both spatially as well as depth over the passage of time, suggests that the decay of aftershocks
perhaps could be controlled by visco-elastic creep in the lower crust. 相似文献
98.
Introduction The displacement field produced by earthquake can be measured on the Earth surface. The displacement field variation with time can be used to study lots of geodynamics parameters such as the Earth′s viscosity structure (Nur and Mavko, 1974; Sun et al, 1994; Deng et al, 1998), after-slip distribution (Shen et al, 1994; Reilinger et al, 2000), etc. Furthermore, earthquake also pro-duces lots of aftershocks, which have nearly the same focal mechanism as the main shock (e.g. Hard… 相似文献
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100.