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1.
Most studies of seismic noise cross-correlation (NCC) have focused on regional/continental scale imaging using empirical surface-wave Green’s functions extracted from primary (0.05–0.08 Hz) and secondary (0.1–0.16 Hz) microseisms. In this work, we present the NCC results at higher frequencies (>0.5 Hz) from 6 months seismic noise recorded by a local array (~4 km aperture) deployed along the Calico fault in the Mojave Desert, California. Both fast and slow propagating waves are observed from the NCC record-sections. We compare the NCCs from sensor pairs that share a common sensor with the records of a borehole shot located very close to this common sensor. The result shows a good match of the slow surface-wave arrivals, indicating that the NCC method is able to recover unbiased surface-wave Green’s functions at local scales. The strong body-wave NCC component is caused by the P waves generated offshore California. Along a SW–NE profile across the fault, we observe apparent P-wave arrivals and their reflections, which can be explained by a low-velocity-zone (LVZ) along the Calico fault. We calculate the LVZ width to be ~ 2.3 km, and the P-wave velocity reduction within the LVZ to be ~35 %. These estimates are consistent with other evidence for a relatively wide LVZ along the Calico fault. 相似文献
2.
Spatial-temporal characterization of the San Andreas Fault by fault-zone trapped waves at seismic experiment site,Parkfield, California 
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下载免费PDF全文 Yong-Gang Li 《地震科学（英文版）》2021,34(3):261-285
In this article, we review our previous research for spatial and temporal characterizations of the San Andreas Fault (SAF) at Parkfield, using the fault-zone trapped wave (FZTW) since the middle 1980s. Parkfield, California has been taken as a scientific seismic experimental site in the USA since the 1970s, and the SAF is the target fault to investigate earthquake physics and forecasting. More than ten types of field experiments (including seismic, geophysical, geochemical, geodetic and so on) have been carried out at this experimental site since then. In the fall of 2003, a pair of scientific wells were drilled at the San Andreas Fault Observatory at Depth (SAFOD) site; the main-hole (MH) passed a ～200-m-wide low-velocity zone (LVZ) with highly fractured rocks of the SAF at a depth of ～3.2 km below the wellhead on the ground level (Hickman et al., 2005; Zoback, 2007; Lockner et al., 2011). Borehole seismographs were installed in the SAFOD MH in 2004, which were located within the LVZ of the fault at ～3-km depth to probe the internal structure and physical properties of the SAF. On September 282004, a M6 earthquake occurred ～15 km southeast of the town of Parkfield. The data recorded in the field experiments before and after the 2004 M6 earthquake provided a unique opportunity to monitor the co-mainshock damage and post-seismic heal of the SAF associated with this strong earthquake. This retrospective review of the results from a sequence of our previous experiments at the Parkfield SAF, California, will be valuable for other researchers who are carrying out seismic experiments at the active faults to develop the community seismic wave velocity models, the fault models and the earthquake forecasting models in global seismogenic regions. 相似文献
3.
ShengLi Mi ShunYun Chen PeiXun Liu XiaoYan Hu KaiYing Wang YuanMin Huang 《中国科学D辑(英文版)》2008,51(10):1436-1445
Studying the effect of geometrically irregular bodies on the mechanical behavior of fault activity is of significance in understanding the seismic activity along a fault zone. By using rock mechanics ex- periment with medium-scale samples, we have studied the effect of fault jogs, the most common irregularity along fault zones, on frictional behavior. The research indicates that extensional fault jog can be easily fractured because of its low strength and the fractured jog has no obvious resistance to fault sliding, and the micro-fractures occurring in the jog are indicative of stick-slip along the faults. The fault zone containing extensional jogs is characterized by velocity weakening and can be described by rate and state friction law. Compressional fault jog makes fault sliding more difficult because of its high fracturing strength, but the micro-fractures occurring in the tensile areas around fault ends at higher stress level can provide necessary condition for occurrence of stick-slip along the faults before the jog is fractured and thus act as precursors of fault instability. Compression jog can be taken as a stable indicator of fault segmentation until the jog is completely fractured and two faults are linked. 相似文献
4.
Hongfeng Yang 《地震科学（英文版）》2015,28(2):151-162
Crustal faults usually have a fault core and surrounding regions of brittle damage, forming a low-velocity zone(LVZ) in the immediate vicinity of the main slip interface. The LVZ may amplify ground motion, influence rupture propagation, and hold important information of earthquake physics. A number of geophysical and geodetic methods have been developed to derive high-resolution structure of the LVZ. Here, I review a few recent approaches, including ambient noise cross-correlation on dense across-fault arrays and GPS recordings of fault-zone trapped waves. Despite the past efforts, many questions concerning the LVZ structure remain unclear, such as the depth extent of the LVZ. High-quality data from larger and denser arrays and new seismic imaging technique using larger portion of recorded waveforms, which are currently under active development, may be able to better resolve the LVZ structure. In addition, effects of the alongstrike segmentation and gradational velocity changes across the boundaries between the LVZ and the host rock on rupture propagation should be investigated by conducting comprehensive numerical experiments. Furthermore, high-quality active sources such as recently developed large-volume airgun arrays provide a powerful tool to continuously monitor temporal changes of fault-zone properties, and thus can advance our understanding of fault zone evolution. 相似文献
5.
通过浅层高分辨率地震探测 ,结合钻孔资料 ,获得了测线处汾河断裂的准确位置 ,几何结构 ,活动性质、时代和速率等参数 ,并对其动力学属性进行了初步的讨论。地震探测揭露出汾河断裂的西支断层 ,为高角度东倾的斜滑断层 ,切割了第四系下部 ,上断点位于地下约 70m处。据钻孔剖面推断有 2条高角度相向而倾的斜滑断层 ,东支位于汾河东岸 ,断至全新统—上更新统 ,其底界面垂直错距约 8m。断裂北段另一个钻孔剖面表明 ,西支断层切割了全新统—上更新统 ,底界面垂直错距约6m。汾河断裂晚更新世以来的平均垂直滑动速率为 0 0 6～ 0 0 8mm/a ,大震平均重复间隔为 5 0～6 7ka 相似文献
6.
琼西北地区的基底速度图象 总被引：4，自引：0，他引：4
利用人工地震测深纵剖面和非纵剖面的资料,对琼西北地区Pg波的走时进行了层析反演,对比了代数重建法和同时迭代重建法的效果.综合了纵剖面的模型后,在三维弯曲界面上重建了基底速度图象,探讨了用射线椭圆评价分辨的途径. 层析成象结果给出了许多有价值的信息,揭示琼西北的结晶基底存在三条北东向断裂和两条北西向断裂,后者是继承性的活动断裂,控制着新生代次级断块的发展与火山活动.地表所推断的东西向王五-文教深大断裂,在该处只呈断续隐伏状显示.该区的基底存在儋县、临高和光村三个高速区,主要反映着基性岩体或花岗侵入体.基底整体性最好的是在儋县-王五地区,破碎程度最严重的是在王五-中和-光村以西的地区. 相似文献
7.
低速带具有“自由表面、低速度、高吸收”的特征,能引起反射波能量减弱,产生很强的频散,造成近地表波场畸变,严重影响地震勘探的精度。而地震采集过程又不可避免遇到以下低速带问题:①低速带存在与否会对地震波传播造成什么影响;②近地表变化大,怎么才能得到精确的低速带参数;③存在低速带时,激发井深、最佳的药量(与子波频率有关)、最佳的耦合(与低速带速度相关)等采集参数会对采集资料的品质产生什么影响。本文通过数值模拟,集中对低速带与地震波激发的井深、速度、子波主频等核心采集参数的关系进行分析研究,同时在低速带背景下对数值模拟的网格、边界等问题也进行了讨论。模拟得到的波场特征及低速带参数影响的机理分析,对做好野外地震波激发,获取高品质的地震资料,具有理论意义和指导作用。 相似文献
8.
ZHANG Zhongjie BAI Zhiming WANG Chunyong TENG Jiwen Lü Qingtian LI Jiliang LIU Yifeng & LIU Zhenkuan . Institute of Geology Geophysics Chinese Academy of Sciences Beijing China . Institute of Geophysics China Seismological Bureau Beijing China . Institute of Deposition Resource Chinese Academy of Geosciences Beijing China . School of Exploration Information China University of Geosciences Beijing China 《中国科学D辑(英文版)》2005,48(9):1329-1336
The Sanjiang area in southwest China is considered as a tectonic intersection belt between the Tethys-Alps and the western Pacific, and has endured three-phase evolution processes: Proto-Tethys,Paleo-Tethys and Meso-Tethys[1―4]. In this area, its tectonics and struc- ture are extremely complicated, and intensively extru-sive deformation and faults are widely developed[1―3]. For that, the area is considered as the ideal na- ture-laboratory to study the evolution of Paleo-Tethys and also … 相似文献
9.
A. S. N. Murty B. Rajendra Prasad P. Koteswara Rao S. Raju T. Sateesh 《Pure and Applied Geophysics》2010,167(3):233-251
2-D shallow velocity structure is derived by travel-time inversion of the first arrival seismic refraction and wide-angle reflection data along the E–W trending Narayanpur–Nandurbar and N–S Kothar–Sakri profiles, located in the Narmada–Tapti region of the Deccan syneclise. Deccan volcanic (Trap) rocks are exposed along the two profiles. Inversion of seismic data reveals two layered velocity structures above the basement along the two profiles. The first layer with a P-wave velocity of 5.15–5.25 km s?1 and thickness varying from 0.7–1.5 km represents the Deccan Trap formation along the Narayanpur–Nandurbar profile. The Trap layer velocity ranges from 4.5 to 5.20 km s?1 and the thickness varies from 0.95 to 1.5 km along the Kothar–Sakri profile. The second layer represents the low velocity Mesozoic sediments with a P-wave velocity of 3.5 km s?1 and thickness ranging from about 0.70 to 1.6 km and 0.55 to 1.1 km along the E–W and N–S profiles, respectively. Presence of a low-velocity zone (LVZ) below the volcanic rocks in the study area is inferred from the travel-time ‘skip’ and amplitude decay of the first arrival refraction data together with the prominent wide-angle reflection phase immediately after the first arrivals from the Deccan Trap formation. The basement with a P-wave velocity of 5.8–6.05 km s?1 lies at a depth ranging from 1.5 to 2.45 km along the profiles. The velocity models of the profiles are similar to each other at the intersection point. The results indicate the existence of a Mesozoic basin in the Narmada–Tapti region of the Deccan syneclise. 相似文献
10.
We present new in situ observations of systematic asymmetry in the pattern of damage expressed by fault zone rocks along sections of the San Andreas,
San Jacinto, and Punchbowl faults in southern California. The observed structural asymmetry has consistent manifestations
at a fault core scale of millimeters to meters, a fault zone scale of meters to tens of meters and related geomorphologic
features. The observed asymmetric signals are in agreement with other geological and geophysical observations of structural
asymmetry in a damage zone scale of tens to hundreds of meters. In all of those scales, more damage is found on the side of
the fault with faster seismic velocities at seismogenic depths. The observed correlation between the damage asymmetry and
local seismic velocity structure is compatible with theoretical predictions associated with preferred propagation direction
of earthquake ruptures along faults that separate different crustal blocks. The data are consistent with a preferred northwestward
propagation direction for ruptures on all three faults. If our results are supported by additional observations, asymmetry
of structural properties determined in field studies can be utilized to infer preferred propagation direction of large earthquake
ruptures along a given fault section. The property of a preferred rupture direction can explain anomalous behavior of historic
rupture events, and may have profound implications for many aspects of earthquake physics on large faults. 相似文献