共查询到20条相似文献，搜索用时 31 毫秒
1.
2.
3.
以2004年内蒙古东乌珠穆沁旗Ms5．9地震为研究对象,对震中区域的地震活动参量b值进行时间扫描计算,Ms5．9地震前b值表现为高值回落;在选取的时空范围内,计算出震中区域平均波速比和地震空间相关长度,Ms5．9地震前波速比变化过程为下降一持续低值一回升发震,地震空间相关长度在震前趋势性上升,分析认为：可以把波速比的和地震空间相关长度的震前变化规律作为同一区域未来地震的预测依据。 相似文献
4.
S. Gautier D. Latorre J. Virieux A. Deschamps C. Skarpelos A. Sotiriou A. Serpetsidaki A. Tselentis 《Pure and Applied Geophysics》2006,163(2-3):431-453
We present the results of a tomographic study performed in the framework of the 3F-Corinth project. The aim of this work is
to better understand the rifting process by imaging the crustal structure of the western Gulf of Corinth. Forty-nine stations
were deployed for a period of six months, allowing us to monitor the microseismicity. Delayed P and S first-arrival times
have been simultaneously inverted for both hypocenter locations and 3-D velocity distributions. We use an improved linearized
tomography method based on an accurate finite-difference travel-time computation to invert the data set. The obtained Vp and
Vs models confirm the presence of a two-layer vertical structure characterized by a sharp velocity gradient lying at 5–7 km
depth, which may be interpreted as a lithological contrast. The shallower part of the crust (down to 5 km depth) is controlled
by the N-S extension and lacks seismicity. The deeper part (7–13 km depth) matches the seismogenic zone and is characterized
by faster and more heterogeneous anomalies. In this zone, the background seismicity reveals a low-angle active surface dipping
about 20° toward the north and striking WNW-ESE. The position of this active structure is consistent with both high Vp/Vs
and low Vp.Vs anomalies identified at 8–12 km depth and suggesting a highly fracturated and fluid-saturated zone. Both the
geometry of the active structure beneath the gulf and the presence of fluids at 8–12 km depth are in accordance with a low-angle
detachment model for the western part of the Gulf of Corinth.
S. Gautier and D. Latorre formerly at Géosciences Azur 相似文献
5.
Fataneh Taghizadeh-Farahmand Forough Sodoudi Narges Afsari Mohammad R. Ghassemi 《Journal of Seismology》2010,14(4):823-836
We computed P and S receiver functions to investigate the lithospheric structure beneath the northwest Iran and compute the Vp/Vs ratio within the crust of this seismologically active area. Our results enabled us to map the lateral variations of the Moho as well as those of the lithosphere–asthenosphere boundary (LAB) beneath this region. We selected data from teleseismic events (Mb?>?5.5, epicentral distance between 30° and 95° for P receiver functions and Mb?>?5.7, epicentral distance between 60° and 85° for S receiver functions) recorded from 1995 to 2008 at 8 three-component short-period stations of Tabriz Telemetry Seismic Network. Our results obtained from P receiver functions indicate clear conversions at the Moho boundary. The Moho depth was firstly estimated from the delay time of the Moho converted phase relative to the direct P wave. Then we used the H-Vp/Vs stacking algorithm of Zhu and Kanamori to estimate the crustal thickness and Vp/Vs ratio underneath the stations with clear Moho multiples. We found an average Moho depth of 48 km, which varies between 38.5 and 53 km. The Moho boundary showed a significant deepening towards east and north. This may reveal a crustal thickening towards northeast possibly due to the collision between the Central Iran and South Caspian plates. The obtained average Vp/Vs ratio was estimated to be 1.76, which varies between 1.73 and 1.82. The crustal structure was also determined by modeling of P receiver functions. We obtained a three-layered model for the crust beneath this area. The thickness of the layers is estimated to be 6–11, 18–35, and 38–53 km, respectively. The average of the shear wave velocity was calculated to be 3.4 km/s in the crust and reaches 4.3 km/s below the Moho discontinuity. The crustal thickness values obtained from P receiver functions are in good agreement with those derived by S receiver functions. In addition, clear conversions with negative polarity were observed at ~8.7 s in S receiver functions, which could be related to the conversion at the LAB. This may show a relatively thin continental lithosphere of about 85 km implying that the lithosphere was influenced by various geodynamical reworking processes in the past. 相似文献
6.
本文提出了一种新的反演方法:通过采用纵、横波走时数据对(从相同的震源产生的P和S波被同一台站记录)来联合反演纵波速度(Vp)和纵、横波速度比(Vp/Vs),然后单独反演横波速度Vs,在反演过程中同时对地震参数进行定位。该方法不需要假设P和S波的射线路径一致,它是沿着P和S波射线路径计算相对慢度扰动值。该方法直接把Vp/Vs作为一个模型参数,由此能获得比采用从独立反演获得的Vp和Vs计算出Vp/Vs的方法更精确的速度比值。该新方法被应用到反演日本东北地区的壳幔速度及波速比结构的研究中,获得了较好的效果。反演结果表明,在日本东北地区,太平洋俯冲板块为一高Vp,高Vs和低Vp/Vs异常区,而在活火山下方的浅部地幔楔以及背弧深部地区为低Vp,低VS和高Vp/VS异常。虽然这些特征在前人的研究中已经报道过,但与前人的研究结果相比,本次研究所获得的Vp/Vs的空间分布具有较小的分散性,同时,它的分布特征能较好的与地震波速度结构相吻合。 相似文献
7.
Chun-Yong Wang Hai Lou Paul G. Silver Lupei Zhu Lijun Chang 《Earth and Planetary Science Letters》2010,289(3-4):367-376
We determined crustal structure along the latitude 30°N through the eastern Tibetan Plateau using a teleseismic receiver function analysis. The data came mostly from seismic stations deployed in eastern Tibet and western Sichuan region from 2004 to 2006. Crustal thickness and Vp/Vs ratio at each station were estimated by the H–k stacking method. On the profile, the mean crustal thickness and Vp/Vs ratio were found to be 62.3 km and 1.74 in the Lhasa block, 71.2 km and 1.79 near the Bangong–Nujiang suture, 66.3 km and 1.80 in the Qiangtang block, 59.8 km and 1.81 in the Songpan–Garze block, and 42.9 km and 1.76 in the Yangtze block, respectively. The estimated crustal thicknesses are consistent with predictions based on the topography and the Airy isostasy, except near the Bangong–Nujiang suture and in the Qiangtang block where the crust is 5–10 km thicker than predicted, indicating that the crust may be denser, possibly due to mafic underplating. We also inverted receiver functions for crustal velocity structure along the profile, which reveals a low S-wave velocity zone in the lower crust beneath the eastern Tibetan Plateau, although the extent of the low-velocity zone varies considerably. The low-velocity zone, together with previous results, suggests limited partial melting and localized crustal flow in the lower crust of the eastern Tibetan Plateau. 相似文献
8.
本研究通过反演241,561条纵波和209,363条横波高质量的地震走时数据,获得了鲜水河、安宁河断裂带的P波、S波以及泊松比的三维结构模型,并结合相位分析与Schuster测试讨论了该断裂带上地震事件的触发与其深部构造以及固体潮所产生的应力变化三者之间的关系.结果表明,鲜水河—安宁河断裂带26.5°N、28°N、29.5°N以及31.5°N四个位置附近存在低速、高泊松比异常,可能暗示着深部流体(包括部分熔融物质)的上涌.这些大范围分布的流体提高了孕震层的孔隙流体压力,削弱了断层面之间摩擦力,在鲜水河—安宁河断裂带形成了一些具有高度地震活动性的区域.此外,相位分析与Schuster测试的结果表明,鲜水河—安宁河断裂带附近的地震触发与固体潮剪切应力的变化密切相关.综合分析的结果表明,固体潮与构造应力对地震触发可能存在某种“合”的关系.在分布着大量流体的区域,地震事件可能对固体潮更加敏感. 相似文献
9.
通过对忻州─泰安人工地震测深剖面Ｐ波、Ｓ波的联合解释，得到沿剖面不同地质单元隆起区与裂陷区、震源区与非震区的速度和波速比结构．鲁西隆起和太行、山西隆起为较均匀的成层构造，地壳厚度分别为３２ｋｍ和４０－４３ｋｍ，波速比为１．７４．中段裂陷区构造变化较大，地壳厚度约３０－３３ｋｍ，波速比为１．７５－１．７７．邢台地震区上地壳下部和中地壳出现高波速比１．７７的异常，与裂陷区东的１．７３形成明显的差异．由此推测，地震的发生不仅与震源区的构造有关，更主要是与震源区岩石的性质有关。 相似文献
10.
本文分析了1975年2月4日海城7.3级地震前后147次地震的资料。结果表明,主震前地震波速比有明显的异常变化。纵横波速比Vp/Vs表现为“下降-回升”的异常形态,负异常至少在主震前四年已出现,最大异常幅度为10％左右,负异常结束后十个月发生主震。主震前波速比异常区较大;而震源附近的小区域,仅在全区波速比回升后的临震前才出现了急剧的负异常。主震前横波速度变化不大,纵波和虚波速度出现异常变化。在一次4.8级强余震前两个月,波速比也出现了负异常。 本文还分析了8次人工爆破,但未发现主震前波速比的异常变化。 关于波速比异常的原因,初步认为是岩石在构造应力的集中作用下,弹性性质发生变化、内部出现大量微裂隙而造成的。 相似文献
11.
Timo Tiira Tomasz Janik Elena Kozlovskaya Marek Grad Annakaisa Korja Kari Komminaho Endre HegedŰs Csaba Attila Kovács Hanna Silvennoinen Ewald BrŰckl 《Pure and Applied Geophysics》2014,171(7):1129-1152
We have studied the lateral velocity variations along a partly buried inverted paleo–rift in Central Lapland, Northern Europe with a 2D wide-angle reflection and refraction experiment, HUKKA 2007. The experiment was designed to use seven chemical explosions from commercial and military sites as sources of seismic energy. The shots were recorded by 102 stations with an average spacing of 3.45 km. Two-dimensional crustal models of variations in P-wave velocity and Vp/Vs-ratio were calculated using the ray tracing forward modeling technique. The HUKKA 2007 experiment comprises a 455 km long profile that runs NNW–SSE parallel to the Kittilä Shear Zone, a major deformation zone hosting gold deposits in the area. The profile crosses Paleoproterozoic and reactivated Archean terranes of Central Lapland. The velocity model shows a significant difference in crustal velocity structure between the northern (distances 0–120 km) and southern parts of the profile. The difference in P-wave velocities and Vp/Vs ratio can be followed through the whole crust down to the Moho boundary indicating major tectonic boundaries. Upper crustal velocities seem to vary with the terranes/compositional differences mapped at the surface. The lower layer of the upper crust displays velocities of 6.0–6.1 km/s. Both Paleoproterozoic and Archean terranes are associated with high velocity bodies (6.30–6.35 km/s) at 100 and 200–350 km distances. The Central Lapland greenstone belt and Central Lapland Granitoid complex are associated with a 4 km-thick zone of unusually low velocities (<6.0 km/s) at distances between 120 and 220 km. We interpret the HUKKA 2007 profile to image an old, partly buried, inverted continental rift zone that has been closed and modified by younger tectonic events. It has structural features typical of rifts: inward dipping rift shoulders, undulating thickness of the middle crust, high velocity lower crust and a rather uniform crustal thickness of 48 km. 相似文献
12.
Wang Andong Ren Yuhe Sun Wenfu Yu Longwei Liang Jingming Cao Tianqing Gu Haoding 《地震学报(英文版)》1988,1(4):60-72
We have obtained altogether heat flux data of 23 drill holes including 2 observational holes of thermal flow in the Haicheng
seismic area. These data show roughly thermal structure of the crust in eastern Liaoning and in the Haicheng seismic area.
The results indicate that there is higher value of heat flow in the belt north by east from Liaoyang to Xiongyue, the average
thermal flux being 8.29× 10−2J/m2·s (2.0 hfu). The average thermal fulx in the Haicheng seismic area is 9.22×102J/m2·s (2.2 hfu).
Comparing with other known geophysical data of the Haicheng seismic area, we give a geophysical section of comprehensive interpretation.
We suppose the low-velocity layer in the lower crust of the Haicheng seismic area is a result from intrusion of large-scale
uper mantle substance. High temperature and low velocity mean that the layer has the nature of plastic mechanics. The focal
region of the Haicheng earthquake is situated right in the upper part of that plastic layer. Obviously, this result is significant
for studying the seismogenic process of the Haicheng earthquake and other intra-plate earthquakes.
We attempt to emphasize that observation of heat flow is necessary for earthquake study.
Gu Haoding did the actual writing. 相似文献
13.
1976年和林格尔6.3级地震前后震兆特征分析 总被引：2，自引：0，他引：2
从时空变化特征、震源参数、地震波谱特征，b值，Vp/Vs,Q值，持续时间衰减比，Ap/As等方面对1976年4月6日和林格尔6．3级地震进行了较为全面的分析，着重分析了地震前后2年左右出现的运动学和动力学变化特征，以提取和林格尔6．3级地震的短临信息，分析后认为此次地震出现的震兆特征与包头6．4级地震，张北6．级地震某些方面有相似处，对探讨分析未来阴山、燕山地震带浅源中强震的孕育过程及提取临震信息，具有参考意义。 相似文献
14.
1978年5月18日海城地震(Ms=6.0)发生在1975年2月4日海城破坏性地震(Ms=7.3)余震区的空区内.1975年2月4日海城7.3级强震发生之后,其余震(Ms2.0)的月频度衰减异常缓慢(P=0.73),而6级地震发生之后 P 值明显增大,即6级地震发生在月频度衰减曲线的拐点上.这次6级地震之前不同于7.3级强震前,在震源区没有丰富的前震活动.6级地震是7.3级强震的最大余震,作者认为它是区域应力在未曾充分破裂的空区内再次集中积累而发生的余震. 相似文献
15.
Prantik Mandal R. K. Chadha N. Kumar I. P. Raju C. Satyamurty 《Pure and Applied Geophysics》2007,164(11):2235-2254
During the last six years, the National Geophysical Research Institute, Hyderabad has established a semi-permanent seismological
network of 5 broadband seismographs and 10 accelerographs in the Kachchh seismic zone, Gujarat, with the prime objective to
monitor the continued aftershock activity of the 2001 Mw7.7 Bhuj mainshock. The reliable and accurate broadband data for the Mw 7.6 (8 Oct., 2005) Kashmir earthquake and its aftershocks from this network, as well as from the Hyderabad Geoscope station,
enabled us to estimate the group velocity dispersion characteristics and the one-dimensional regional shear-velocity structure
of peninsular India. Firstly, we measure Rayleigh- and Love-wave group velocity dispersion curves in the range of 8 to 35
sec and invert these curves to estimate the crustal and upper mantle structure below the western part of peninsular India.
Our best model suggests a two-layered crust: The upper crust is 13.8-km thick with a shear velocity (Vs) of 3.2 km/s; the
corresponding values for the lower crust are 24.9 km and 3.7 km/sec. The shear velocity for the upper mantle is found to be
4.65 km/sec. Based on this structure, we perform a moment tensor (MT) inversion of the bandpass (0.05–0.02 Hz) filtered seismograms
of the Kashmir earthquake. The best fit is obtained for a source located at a depth of 30 km, with a seismic moment, Mo, of
1.6 × 1027 dyne-cm, and a focal mechanism with strike 19.5°, dip 42°, and rake 167°. The long-period magnitude (MA ~ Mw) of this earthquake is estimated to be 7.31. An analysis of well-developed sPn and sSn regional crustal phases from the bandpassed
(0.02–0.25 Hz) seismograms of this earthquake at four stations in Kachchh suggests a focal depth of 30.8 km. 相似文献
16.
用多震相地震走时成像法反演郯庐断裂带鲁苏皖段及邻区三维地壳速度结构。一些地区如郯庐断裂带临沭到定远及以东地区在中地壳的20~25km出现低速层,一些地区莫霍面埋深有变化。浅层速度结构的分段与断裂活动的分段相一致,表明新沂到泗洪是活动断裂的闭锁段。对比1668年山东郯城8级地震区和研究区的深部速度结构,结合与郯庐带相交的断裂、地震活动、活动断裂的闭锁段、中地壳低速层及莫霍面深度变化,综合判断郯庐断裂带江苏段未来可能发生大震的地区为33.4°~34.1°N,118.2°~118.8°E,重点是宿迁、沭阳、泗阳和泗洪。震级估计可达8级。 相似文献
17.
Prantik Mandal R. K. Chadha N. Kumar I. P. Raju C. Satyamurty 《Pure and Applied Geophysics》2007,164(10):1963-1983
During the last six years, National Geophysical Research Institute, Hyderabad has established a semi-permanent seismological
network of 5–8 broadband seismographs and 10–20 accelerographs in the Kachchh seismic zone, Gujarat with a prime objective
to monitor the continued aftershock activity of the 2001 Mw 7.7 Bhuj mainshock. The reliable and accurate broadband data for the 8 October Mw 7.6 2005 Kashmir earthquake and its aftershocks from this network as well as Hyderabad Geoscope station enabled us to estimate
the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the Peninsular India.
Firstly, we measure Rayleigh-and Love-wave group velocity dispersion curves in the period range of 8 to 35 sec and invert
these curves to estimate the crustal and upper mantle structure below the western part of Peninsular India. Our best model
suggests a two-layered crust: The upper crust is 13.8 km thick with a shear velocity (Vs) of 3.2 km/s; the corresponding values
for the lower crust are 24.9 km and 3.7 km/sec. The shear velocity for the upper mantle is found to be 4.65 km/sec. Based
on this structure, we perform a moment tensor (MT) inversion of the bandpass (0.05–0.02 Hz) filtered seismograms of the Kashmir
earthquake. The best fit is obtained for a source located at a depth of 30 km, with a seismic moment, Mo, of 1.6 × 1027 dyne-cm, and a focal mechanism with strike 19.5°, dip 42°, and rake 167°. The long-period magnitude (MA ~ Mw) of this earthquake is estimated to be 7.31. An analysis of well-developed sPn and sSn regional crustal phases from the bandpassed
(0.02–0.25 Hz) seismograms of this earthquake at four stations in Kachchh suggests a focal depth of 30.8 km. 相似文献
18.
通过对1976年9月23日巴音木仁6.2级地震前后2年左右记录资料的地震活动性、地震活动图像时空变化特征及测震学指标等变化特征的分析,发现巴音木仁6.2级地震活动性从震前半年左右时间内开始明显增强,出现了典型前兆震群-磴口震群,地震活动图像出现了条带及空区特征,这种特征在震后有向东北迁移的倾向,可能对1979年五原6.0级地震有着重要推动作用。同时震前b值、Vp/Vs、Q值等也出现了明显的异常。此震所出现的震兆特征对探讨分析浅源中强地震的孕育过程及提取临震信息有一定参考价值。 相似文献
19.
Athanassios Ganas Zafeiria Roumelioti Vassilios Karastathis Konstantinos Chousianitis Alexandra Moshou Evangelos Mouzakiotis 《Journal of Seismology》2014,18(3):433-455
We investigate mainshock slip distribution and aftershock activity of the 8 January 2013 M w?=?5.7 Lemnos earthquake, north Aegean Sea. We analyse the seismic waveforms to better understand the spatio-temporal characteristics of earthquake rupture within the seismogenic layer of the crust. Peak slip values range from 50 to 64 cm and mean slip values range from 10 to 12 cm. The slip patches of the event extend over an area of dimensions 16?×?16 km2. We also relocate aftershock catalog locations to image seismic fault dimensions and test earthquake transfer models. The relocated events allowed us to identify the active faults in this area of the north Aegean Sea by locating two, NE–SW linear patterns of aftershocks. The aftershock distribution of the mainshock event clearly reveals a NE–SW striking fault about 40 km offshore Lemnos Island that extends from 2 km up to a depth of 14 km. After the mainshock most of the seismic activity migrated to the east and to the north of the hypocenter due to (a) rupture directivity towards the NE and (b) Coulomb stress transfer. A stress inversion analysis based on 14 focal mechanisms of aftershocks showed that the maximum horizontal stress is compressional at N84°E. The static stress transfer analysis for all post-1943 major events in the North Aegean shows no evidence for triggering of the 2013 event. We suggest that the 2013 event occurred due to tectonic loading of the North Aegean crust. 相似文献
20.
Zhang Lu Bai Zhiming Xu Tao Wu Zhenbo Huang Minfu Yu Guiping Chen Junlei Zheng Mengjie 《中国科学:地球科学(英文版)》2020,63(9):1294-1308
Geological studies show that the southern part of Ailaoshan-Red River shear zone(ALSRRSZ) has experienced complex metallogenic processes and multi-stage non-uniform uplifting, called oblique uplifting since the Cenozoic. To detect the deep structure and geodynamic background beneath Daping, Chang'an and other gold and polymetallic deposits in this area, we carried out a high-density short-period seismic array survey in southern Yunnan province. The array used is approximately240 km long with an interval of 500 m between two adjacent stations. Based on the data collected by the array, we used H-κstacking and common conversion point(CCP) methods of receiver functions to reveal the fine crustal structure beneath this array,which was located from Lvchun(western end) to the east and ended in Maguan. The three main conclusions are as follows.(1)The average crustal thickness is approximately 37 km and the Vp/Vsratio is 1.75. However, the thickness and Vp/Vsratio of the Ailao Mountain are rather greater or higher than those of the western Lanping-Simao Basin and eastern South-China block.These results may indicate that the crust is rich in ferromagnesian minerals or has a thermal fluid anomaly after orogenic movement.(2) There are two obvious inclined interfaces beneath the Ailao Mountain in the mid-upper crust, which suggests that strong deformation occurred there during the orogenic period. Some evidences, such as the weak converted-wave Pms phase from the Moho, low P-wave velocities of the upper mantle, high surface heat flow values, and generally developed hot springs,indicate that a strong crust-mantle interaction exists in the southern segments of the Ailaoshan-Red River shear zone. These interactions include a diapir of mantle-sourced magma(stronger in the east than that in the west), lateral collision from the Indian Plate, and the differential uplift caused by the strike-slip movement of the Red River Fault. All of above deep processes led to the Cenozoic oblique uplifting of Ailao Mountain.(3) By combining the location of the deposits on the surface, characteristics of the average crustal Vp/Vsratio, hypocenters of the small earthquakes along the research profile, Moho shape, and horizontal variations of the Pms phase amplitudes, we speculate that the Ailaoshan Fault was the upgoing conduit for metallogenic magma and played a significant role in the Cenozoic development of the multiform metal deposits around the Ailao Mountain area. 相似文献