共查询到20条相似文献，搜索用时 46 毫秒
1.
１９９５年７月２２日甘肃永登５．８级地震的震源机制董积平（国家地震局兰州地震研究所，兰州７３００００）主题词：甘肃，震源机制，永登１９９５年７月２２日６时４４分，甘肃省永登县发生了Ｍｓ５．８地震。经甘肃省地震监测台网测定，该次地震的震中位置为北纬３６... 相似文献
2.
永登5.8级地震和天祝—古浪5.4级地震前S波分裂特征 总被引：1，自引：0，他引：1
应用ＣＤＳＮ台网兰州数字台的记录和中法合作建立的朗索数字台的记录,研究了１９９５年７月２２日甘肃永登５．８级地震和１９９６年６月１日天祝－古浪５．４级地震前台剪切波分裂的特征。结果表明,在永登地震前大约１年的时间延迟和偏振方向很快恢复。因此,可以认为,此次地震前ＮＷ向,地震后剪切波分裂时间延迟和偏振方向很快恢复。因此,可以认为,此次地震前Ｓ波分裂方向的前兆特征是明显的。对于天祝－古浪５．４级地震, 相似文献
3.
甘肃近期2次中强震前后震源区微震尾波（Qc）的变化特征 总被引：4，自引：0，他引：4
利用张掖台网和天祝－古浪台网的记录资料研究了１９８８年１１月２２日肃南５．７级地震和１９９６年６月１日天祝－古浪５．４级地震前台震源区微震尾波Ｑｃ值的变化特征,结果表明：５．７级地震前源及邻近地区介质１／Ｑｃ值趋于一致,认为这是该次地震的一种前兆表现,结合该次地震的震源机制和构造情况进行了讨论。天祝－古浪５．４级地震震源区附近地区微震尾波Ｑｃ值民频率的关系表明,这一地区属于构这活动地区。 相似文献
4.
利用短量反演方法反演了１９９６年６月１日天祝－古浪５．４级地震序列的震源机制,并与该区小震综合断层面解进行了比较,在此基础上讨论了该地震前后震源区应力场的变化特征。 相似文献
5.
１９９５年７月９日青海共和５．３级地震的震源机制董积平（国家地震局兰州地震研究所，兰州７３００００）主题词青海，震源机制，共和１９９５年７月９日２３时５６分，青海共和发生了ＭＳ５．３级地震。经国家地震局定位及甘肃省地震监测台网测定，该次地震的震中位置... 相似文献
6.
利用单台数字地震记录反演天祝—古浪5.4级地震矩张量 总被引：2，自引：0，他引：2
利用单台３分向数字化记录反演了１９９６年６月１日甘肃天祝－古浪５．４级地震的矩张量,并对所得结果与用Ｐ波被动符合的结果进行了比较。结果表明,二具有很好的一致性。结合谝地震的震源机制和震源区的断层的构造情况,认为该地震是在ＮＥ－ＳＷ的压应力作用下,近ＥＷ向的源原西断层天祝－古浪段左旋破裂错动的结果。由于我们得出的结果只是利用了记录波形的最初几个波形,因此它基本反映了该地震的初始破裂错动情况。 相似文献
7.
张北地震前地磁空间相关异常特征 总被引：2，自引：1，他引：1
应用地磁空间相关方法对华北地区１９９６年１月至１９９８年１月地磁核旋定点（北京时２１ｈ）观测数据的分析研究表明,１９９８年１月１０日张北ＭＳ６．２地震和１９９６年５月３日内蒙古包头ＭＳ６．４地震前存在地磁空间相关低值异常。 相似文献
8.
１９９１年至１９９４年甘肃地区发生的部分地震的震源机制解根据甘肃省地震台网测定，１９９１年１月２日在青海省祁连境内发生了一次５．１级地震，震中位于北纬３８°６＇，东经９９°５４＇。１９９１年１０月１日在青海省门源境内发生了一次５．２级地震，震中位于北... 相似文献
9.
10.
甘肃永登5.8级地震前兆异常特征及天祝—古浪5.4级地城中短期预报 总被引：1，自引：0，他引：1
综合分析了１９９５年７月２２日甘肃泳登５．８级地夺前兆地震时空分布特征,主要表现为异常数量多、分布广、密度大、震后响应性异常显,且时空分布具有成组性、空间分布具有相对稳定性。这可能与该区中强城成丛活动方式有关。此研究结果在１９９６年６月１日甘肃天祝－古浪５．４级地震中短期预报中发挥了作用。 相似文献
11.
收集、整理四川省地震台网2013年5月至2017年9月产出的震相观测报告数据,采用单台多震和达法,重点分析2017年8月8日九寨沟MS 7.0强震前龙门山断裂带中北段地区波速比变化特征。结果表明：龙门山断裂带中段西侧的茂县地震台,在发震前2年左右,波速比出现一次持续时间约一年半的下降异常;发震前半年左右,波速比出现明显回返特征,波速比回返至均值上下时即发生九寨沟MS 7.0地震;震源区周边其他6个地震台波速比在发震前变化较平稳。茂县地震台波速比低值异常对判定九寨沟MS 7.0强震前龙门山断裂带中北段可能存在孕震体具有重要参考价值。 相似文献
12.
P. Mandal Jainendra S. Joshi Sudesh Kumar Rajendra Bhunia B. K. Rastogi 《Pure and Applied Geophysics》2004,161(8):1635-1654
On 26 January, 2001 (03:46:55,UT) a devastating intraplate earthquake of Mw 7.7 occurred in a region about 5 km NW of Bhachau, Gujarat (23.42°N, 70.23°E). The epicentral distribution of aftershocks defines a marked concentration along an E-W trending and southerly dipping (45°) zone covering an area of (60 × 40) km2. The presence of high seismicity including two earthquakes of magnitudes exceeding 7.7 in the 200 years is presumed to have caused a higher level of shallow crustal heterogeneity in the Kutch area; a site lying in the seismic zone V (zone of the highest seismicity for potentially M8 earthquakes) on the seismic zoning map of India. Attenuation property of the medium around the epicentral area of the Bhuj earthquake covering a circular area of 61,500 km2 with a radius of 140 km is studied by estimating the coda-Qc from 200 local earthquakes of magnitudes varying from 3.0–4.6. The estimated Q0 values at locations in the aftershock zone (high seismicity) are found to be low in comparison to areas at a distance from it. This can be attributed to the fact that seismic waves are highly scattered for paths through the seismically active and fractured zone but they are well behaved outside the aftershock zone. Distribution of Q0 values suggests that the local variation in Q0 values is probably controlled by local geology. The estimated Q0 values at different stations suggest a low value of Q=(102 ± 0.80)*f(0.98 ± 0.02) indicating an attenuative crust beneath the entire region. The frequency-dependent relation indicates a relatively low Qc at lower frequencies (1–3 Hz) that can be attributed to the loss of energy due to scattering attenuation associated with heterogeneities and/or intrinsic attenuation due to fluid movement in the fault zone and fluid-filled cracks. The large Qc at higher frequencies may be related to the propagation of backscattered body waves through deeper parts of the lithosphere where less heterogeneity is expected. Based on the attenuation curve estimated for Q0=102, the ground acceleration at 240 km distance is 13% of 1 g i.e., 0.13 g agreeing well with the ground acceleration recorded by an accelerograph at Ahmedabad (0.11 g). Hence, it is inferred that the Q0 value obtained from this study seems to be apt for prediction of ground motion for the region. 相似文献
13.
Shanxi Graben is in the middle part of the North China Craton, from south to north. With the teleseismic data recorded by Regional Seismograph Networks and the temporary ZBnet-W Seismic Array around east part of Shanxi Graben, we measured the crustal thickness and vP/vS ratio beneath each station using the H-κ stack of receiver functions. The observed crustal thickness shows obvious lateral variation, increasing gradually from east to west in the Shanxi Graben. Beneath the Shanxi Graben the crust is relatively thicker than both sides of the south and the north. In addition, the vP/vS ratio in the north of study zone is higher than that in the south. The highest vP/vS ratio exists in the crust of the Xinding basin and the Datong basin. Our study also suggests that high velocity ratio might result from the strong activities of the magmation and volcanism. 相似文献
14.
In this paper we study the variation of Vp/Vs and Poisson's ratio (δ) in the Yellowstone National Park region, using earthquakes which were well recorded by a local seismic network. We find that the average Vp/Vs value within the geothermally active Yellowstone caldera is about 7% lower than in the area outside the caldera. Within the caldera itself there may be a further 2–7% reduction of Vp/Vs in the hydrothermally active Norris Geyser Basin, the Upper and Lower Geyser Basins, and the Yellowstone Lake and Mud Volcano regions. After considering various possible causes for Vp/Vs changes, such as geologic and structural differences, thermal effects, partial melting, and hydrothermal activity, we conclude that the most plausible explanation for the observed Vp/Vs reduction is the presence of hot-water at temperatures and pore-pressures near the water steam transition in the caldera geothermal reservoirs. 相似文献
15.
A tomographic study of the V
p and V
p/V
s structures in the crust and upper mantle beneath the Taiwan region of China is conducted by simultaneous inversion of P and
S arrival times. Compared with the previous tomographic results, the spherical finite difference technique is suitable for
the strong heterogeneous velocity structure, and may improve the accuracy in the travel time and three-dimensional ray tracing
calculations. The V
p and V
p/V
s structures derived from joint inversion and the relocated earthquakes can provide better constraints for analyzing the lateral
heterogeneity and deep tectonic characters in the crust and upper mantle. Our tomographic results reveal significant relations
between the seismic wavespeed structure and the tectonic characters. In the shallow depth, sedimentary basins and orogen show
distinct wavespeed anomalies, with low V
p, high V
p/V
s in basins and high V
p, low V
p/V
s in orogen. As the suture zone of Eurasian Plate and Philippine Sea Plate, Longitudinal Valley is characterized by a significant
high V
p/V
s anomaly extending to the middle-lower crust and upper mantle, which reflects the impact of rock cracking, partial melting,
and the presence of fluids. In the northeast Taiwan, the V
p, V
p/V
s anomalies and relocated earthquakes depict the subducting Philippine Sea Plate under the Eurasian Plate. The high V
p of oceanic plate and the low V
p, high V
p/V
s atop the subducted oceanic plate extend to 80 km depth. Along the east-west profiles, the thickness of crust reaches 60 km
at the east of Central Range with eastward dipping trend, which reveals the eastward subduction of the thickened and deformed
crust of the Eurasian continental plate.
Supported by Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX3-SW-234-2), National Basic Research
Program of China (Grant No. 2007CB411701), National High Technology Research and Development Program of China (Grant No. 2006AA09A101-0201)
and National Natural Science Foundation of China (Grant Nos. 40804016, 40704013) 相似文献
16.
17.
Ultrasonic compressional wave velocity Vp and quality factor Qp have been measured in alkali basalt, olivine basalt and basic andesite melts in the frequency range of 3.4–22 MHz and in the temperature range of 1100–1400°C. Velocity and attenuation of the melts depend on frequency and temperature, showing that there are relaxation mechanisms in the melts. Complex moduli are calculated from the ultrasonic data. The results fit well a complex modulus of Arrhenius temperature dependence with log-normal Gaussian distribution in relaxation times of attenuation. The analysis yields average relaxation time, its activation energy, relaxed modulus, unrelaxed modulus and width of Gaussian distribution in relaxation times. Relaxed modulus is smaller (17.5 GPa) for basic andesite melt of high silica and high alumina contents than for the other two basalt melts (18.1–18.4 GPa). The most probable relaxation times decrease from ～ 3 × 10?10 s for basic andesite to ～ 10?11 s for alkali basalt at 1400°C. Activation energies of attenuation, ranging from 270 to 340 kJ mol?1 in the three melts, are highest in basic andesite. Longitudinal viscosity values and their temperature dependences are also calculated from Vp and Qp data. The volume viscosity values are estimated from the data using the shear viscosity values. Longitudinal, volume and shear viscosities and their activation energies are highest in the basic andesite melt of the most polymerized structure. 相似文献
18.
利用布设于兴蒙造山带诺敏河火山群地区的宽频带流动地震台站资料,基于接收函数方法,获取了该地区的地壳厚度与波速比值.研究结果显示,该地区的地壳厚度介于32~38 km,莫霍面深度在空间上分布特征与五大连池为中心的火山带分布具有较好的一致性：沿着火山带延展方向地壳较薄.该地区的波速比介于1.74~1.84,波速比在空间上与地壳厚度变化具有一致性：高波速比主要集中于靠近五大连池火山带地区,向诺敏河火山和小古里河火山延展.研究认为：诺敏河火山与五大连池火山带可能具有相同的岩浆来源,可能与富钾岩石圈地幔拆沉作用造成的地幔热物质上涌有关.研究区地壳厚度与波速比呈现负相关关系,暗示该地区可能发生过岩浆底侵作用. 相似文献
19.
《Physics of the Earth and Planetary Interiors》1979,18(4):309-318
On November 7, 1976, an earthquake of the strike-slip fault type, and of magnitude 6.7, occurred at two mountainous localities, Yanyuan and Ninglang, in the border region of the Szechuan and Yunnan Provinces, China. One year before the earthquake, a prediction was made as to the magnitude and location of the impending earthquake by the present authors, on the basis of the results of a general survey of an area of about 20,000 km2 for Vp/Vs ratio variations. The prediction of time of occurrence was made afterwards by the combined analysis of results of observations of some other precursory phenomena. The actual occurrence of the event was generally considered as being in agreement with the prediction.The present study may be taken as a new example for the detection of Vp/Vs ratio variations prior to an earthquake of the strike-slip fault type. By considering the difference between the shear rupture and stick-slip motion and the anisotropy induced by dilatancy, a preliminary discussion is made concerning the related results. 相似文献
20.
收集整理了四川省地震台网1990—2012年产出的地震直达波震相数据, 利用单台多震和达法对2008年汶川MS8.0地震前后四川地区的波速比变化特征进行了分析研究(共筛选出13个数据量较为丰富、 连续性较好的台站). 结果显示: 其中位于龙门山断裂中北段西侧的4个台站, 震前出现长达7年左右的中长期波速比低值异常; 其它9个台站的波速比震前变化基本稳定. 震前波速比出现异常的4个台站的分布与汶川MS8.0地震孕震区范围大体一致, 从而为研究汶川MS8.0地震前是否存在地壳介质特性的时间变化过程, 提供了有力的判定依据. 相似文献