首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 234 毫秒
1.
Source parameters of the earthquakes of the Baikal rift system   总被引：1，自引：0，他引：1  
The dynamic parameters of the earthquake source—the seismic moment, the moment magnitude, the source radius, the stress drop, and the amplitude of displacement—are determined by the amplitude Fourier spectra of the body shear waves (S-waves) for 62 earthquakes of the Baikal rift system with the energy class of K P = 9.1–15.7. In the calculations I used the classical Brune model. The seismic moment of the earthquakes being investigated changes from 3.65 × 1011 N m to 1.35 × 1018 N m, and the radii of earthquake sources vary from 390 m to 1.84 km. The values of the drop in stress Δσ grow with an increase in the seismic moment up to 1.7 × 108 Pa. For the group of weak earthquakes (M w = 1.7–3.3), extremely low values of the drop in stress 103–104 Pa are observed. The maximum amplitude of displacement in the source amounts to 5.95 m. The empirical equations between the seismic moment and the other dynamic parameters of the source are determined. The regional dependence of the seismic moment and energy class is obtained: log M 0 ± 0.60 = 1.03K P + 3.17. The character of the relationship between the seismic moment and the corner frequency indicates that the classical scaling law of the seismic spectrum for the earthquakes in question is not fulfilled. The obtained estimates of the dynamic parameters are in satisfactory agreement with the published data concerning the analogous parameters of the other rift zones, which reflects the general regular patterns of the destruction of the lithosphere and the seismicity in the extension zones of the lithosphere.  相似文献   

2.
—?An intriguing observation in Greenland is a clear spatial correlation between seismicity and deglaciated areas along passive continental margins, a piece of evidence for earthquake triggering due to postglacial rebound. Another piece of evidence for induced seismicity due to deglaciation derives from earthquake source mechanisms. Sparse, low magnitude seismicity has made it difficult to determine focal mechanisms from Greenland earthquakes. On the basis of two normal faulting events along deglaciated margins and from the spatial distribution of epicenters, earlier investigators suggested that the earthquakes of Greenland are due to postglacial rebound. This interpretation is tested here by using more recent data. Broadband waveforms of teleseismic P waves from the August 10, 1993 (m b = 5.4) and October 14, 1998 (m b = 5.1) earthquakes have been inverted for moment tensors and source parameters. Both mechanisms indicate normal faulting with small strike-slip components: the 1993 event, strike = 348.9°, dip = 41.0°, rake =?56.3°, focal depth = 11?km, seismic moment = 1.03?×?1024 dyne-cm, and M w = 5.3; the 1998 event, strike = 61.6°, dip = 58.0°, rake =?95.5°, focal depth = 5?km, seismic moment = 5.72?×?1023 dyne-cm, and M w = 5.1. These and the two prior events support the theory that the shallow part of the lithosphere beneath the deglaciated margins is under horizontal extension. The observed stress field can be explained as flexural stresses due to removal of ice loads and surface loads by glacial erosion. These local extensional stresses are further enhanced by the spreading stress of continental crust and reactivate preexisting faults. Earthquake characteristics observed from Greenland suggest that the dominant seismogenic stresses are from postglacial rebound and spreading of the continental lithosphere.  相似文献   

3.
On May 21, 2021, an MS6.4 earthquake occurred in Yangbi, Yunnan province, China, which exhibited typical foreshock-mainshock-aftershock characteristics. To better understand the velocity structure of the focal area and adjacent fault zones, Pg/Sg travel times at 12 seismic stations for the local earthquakes with ML ≥ 1.5 from 2009–2019 and the Yangbi sequence in May of 2021 were used to invert the three-dimensional (3D) structures for both vP and vP/vS. The obtained structure extends deeply to 15 km for area (25°N–26.5°N, 99.5°E–101°E) at a horizontal resolution of 10× 10 km, and the accuracy of the vP velocity was verified using airgun signals excited by the Binchuan Airgun Transmitting Seismic Station (BATSS). The resulting vP and vP/vS images correlate with existing fault zones and the Yangbi sequence, including: (1) The shallow velocity structure at 0 km agrees with local topography, where the Binchuan basin exhibits low-vP and high-vP/vS values. From 3–15 km, vP and vP/vS show variations, and the boundaries are consistent with the main faults (e.g., the Weixi-Qiaohou-Weishan, Honghe, and Chenghai faults). (2) The largest foreshock (MS5.6), mainshock (MS6.4), and largest aftershock (MS5.2) occurred near the boundaries where both vP and vP/vS have clear contrasts. (3) Small earthquakes are also concentrated in the transition zone between high- and low-vP and vP/vS anomalies, and are biased toward low-vP/vS zones. (4) Boundaries in vP and vP/vS are observed at 20 km west of the Weixi-Qiaohou-Weishan fault, indicating that there may exist one hidden fault.  相似文献   

4.
Using the Cut And Paste (CAP) method, we invert the focal mechanism of 38 moderate earthquakes (MS ≥ 3.0) recorded by Yunnan seismic network and analyze the corresponding focal mechanism consistency based on the minimum spatial rotation angle. Our results indicate that the MS 6.4 mainshock is induced by a lateral strike slip fault (with a rake angle of ～ ?165°) and a little normal-faulting component event along a nearly vertical plane (dipping angle～ 79° and strike ～138°). Combining our results with high resolution catalog, we argue that the seismogenic fault of this earthquake sequence is a secondary fault western to the major Weixi-Qiaohou-Weishan fault. The focal mechanism evolution can be divided into three periods. During the first period, the foreshock sequence, the focal mechanism consistency is the highest (KA<36°); during the second period which is shortly after the mainshock, the focal mechanism shows strong variation with KA ranging from 8° to 110°; during the third period, the seismicity becomes weak and the focal mechanism of the earthquakes becomes more consistent than the second period (18°<KA<73°). We suggest that the KA, to some extent, represents the coherence between local tectonic stress regime and the stress state of each individual earthquake. Furthermore, high focal mechanism consistency and high linearity of seismic distribution may serve as indicators for the identification of foreshock sequence.  相似文献   

5.
Results are reported from the ongoing 2007–2008 work using the method of long-term earthquake prediction for the Kuril-Kamchatka arc based on the patterns of seismic gaps and the seismic cycle. This method was successful in predicting the M S = 8.2 Simushir I. (Middle Kuril Is.) earthquake occurring in the Simushir I. area on November 15, 2006. An M S = 8.1 earthquake occurred in the same area on January 13, 2007. We consider the evolution of the seismic process and determine the common rupture region of the two earthquakes. The sequence of M ≥ 6.0 aftershocks and forecasts for these are given. We provide a long-term forecast for the earthquake-generating zone of the Kuril-Kamchatka arc for the next five years, April 2008 to March 2013. Explanations are given for the method of calculation and prediction. The probable locations of future M ≥ 7.7 earthquakes are specified. For all segments of the earthquake-generating zone we predict the expected phases of the seismic cycle, the rate of low-magnitude seismicity (A10), the magnitudes of moderate-sized earthquakes to be expected, with probabilities of 0.8, 0.5, and 0.15, their maximum possible magnitudes, and the probabilities of occurrence of great (M ≥ 7.7) earthquakes. The results of these forecasts are used to enhance seismic safety.  相似文献   

6.
The Yangbi MS6.4 earthquake occurred on May 21, 2021 in western Yunnan, China, where moderate earthquakes strike frequently. It exhibited a typical “foreshock-mainshock-aftershock” sequence and did not occur on a pre-existing active fault. The seismogenic environment and mechanism of this earthquake have aroused considerable research attention. In this study, we obtain the three-dimensional vP, vS and vP/vS images using the vP/vS consistency-constrained double-difference tomography method, which improves the accuracy of vP/vS models. We focus on characteristics of vP/vS images in areas with a lateral resolution of 0.1°, and reveal the seismogenic environment of the Yangbi MS6.4 earthquake. The conclusions are as follows: (1) Low velocity and high-vP/vS anomalies are revealed at different depths around the northern segment of the Red River fault. vS and vP/vS images along the Weixi-Qiaohou-Weishan fault and the buried faults on its west show obviously segmented feature. (2) The source region of the Yangbi MS6.4 earthquake is located in a low-vP/vS zone implying high medium strength. High-vP/vS anomalies in its NW direction indicate cracks development and the existence of fluids or partial melts, which are unfavorable for stress accumulation and triggering large earthquakes. Such conditions have also prevented the earthquake sequence from extending northwestward. (3) With the southeastward extrusion of materials from the Tibetan Plateau, fluid migration was blocked by the low-vP/vS body in the source region. The high-vP/vS anomaly beneath the source region may implies that the fluids or partial melts in the middle and lower crust gradually weakened medium strength at the bottom of the seismogenic layer, and preparing the largest foreshock in the transition zone of high to low vP/vS. Meanwhile, tectonic stress incessantly accumulated in the brittle upper crust, eventually led to the MS6.4 earthquake occurrence.  相似文献   

7.
We consider the results of reconstructing the stress-strain state of the Earth’s crust in South Baikal from the focal mechanism data for the Kultuk earthquake of August 27, 2008 (M w = 6.3) and its aftershocks. The source parameters of the main shock were determined by calculating the seismic moment tensor. The focal mechanism solutions of 32 aftershocks (M w ≥ 2.3) were obtained through the deployment of a local seismic network at South Baikal. It is found that the main shock and first aftershocks (August–September) gave rise to the activation of latitudinal fragments of the segmented near-edge fault, and the sources of the consequent aftershocks were dominated by the NW-striking planes related to the small intrabasin structures. The calculations of seismotectonic deformations based on the data on the focal mechanisms of the earthquakes show that the area of activation is dominated by the transtension regime (with deformation in the form of extension with shear). The epicentral and hypocentral fields of the aftershocks and the mechanisms of their sources reflect the complex tectonic structure of the source zone of the Kultuk earthquake, which exhibits a clear subvertical zonality of the local seismically active volume and a wedge-shaped area of crustal destruction.  相似文献   

8.
Broadband P and S waves source spectra of 12 MS5.0 earthquakes of the 1997 Jiashi, Xinjiang, China, earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these earthquakes have been estimated through measuring the corner frequency of the source spectra. Direction of rupture propagation of the earthquake faulting has also been inferred from the azimuthal variation of the corner frequency. The main results are as follows: ①The rupture size of MS6.0 strong earthquakes is in the range of 10～20 km, while that of MS=5.0～5.5 earthquakes is 6～10 km.② The static stress drop of the swarm earthquakes is rather low, being of the order of 0.1 MPa. This implies that the deformation release rate in the source region may be low. ③ Stress drop of the earthquakes appears to be proportional to their seismic moment, and also to be dependent on their focal mechanism. The stress drop of normal faulting earthquakes is usually lower than that of strike-slip type earthquakes. ④ For each MS6.0 earthquake there exists an apparent azimuthal variation of the corner frequencies. Azimuthally variation pattern of corner frequencies of different earthquakes shows that the source rupture pattern of the Jiashi earthquake swarm is complex and no uniform rupture expanding direction exists.  相似文献   

9.
应用中国地震局地球物理研究所和蒙古科学院天体和地球物理研究中心合作编制的蒙古国及邻区M≥3.5的地震目录,研究了中蒙弧地区的地震活动性特征.结果表明,与中国大陆的“南北地震带”相对应,研究区地震总体分布大致以107°E为界,呈现西强东弱的特点,7级以上的强震集中于贝加尔湖、萨彦、阿尔泰以及天山地区,107°E以东,除纬度40°线附近（燕山地震带）地震较集中且强度大之外,其它地区地震稀少,强度也低.通过断层的野外调查和本地区震源机制解,进一步研究了该地区地震活动性特征的构造应力场及地球动力学成因.研究区大部份地震都是走滑型断层活动的地震.逆断层活动的地震主要分布于中国的天山地区和中蒙边境一带的阿尔泰山地区,正断层活动的地震主要分布于俄罗斯的贝加尔湖裂谷带,走滑兼倾滑断层活动的地震主要分布在研究区域的西部地区.研究区域内的大部份地区主压应力轴（P）的倾角都小于30°,为水平或近水平的构造应力场,自西向东主压应力轴的走向从近南-北方向逐渐转为北东-南西方向.断层的野外调查、震源机制解和区域构造应力场的方向表明,中蒙弧地区主要来自西南面的印度洋板块向北偏东方向的碰撞挤压,通过青藏高原传递到本区,来自东面太平洋板块的影响已较微弱,这是研究区地震活动西强东弱、8级以上强震都发生在西部的主要原因.  相似文献   

10.
This is an attempt to analyze the current lithospheric stress pattern in the Baikal rift in terms of nonlinear dynamics as an open self-organizing system in order to gain more insights into the general laws of regional seismicity. According to the suggested approach, the stress pattern inferred from seismic moments of 70,000 MLH ≥ 2.0 events that occurred in the region between 1968 and 1994 is presented as a phase portrait in the phase spaces of the seismic moments. The obtained phase portrait of the system evolution fits well a scenario with triple equilibrium bifurcation where stress bifurcations account for the frequency of M > 5.5 earthquakes. Extrapolation of the results into the nearest future indicates probability of such a bifurcation (a catastrophe of stress), i.e., there is growing risk that M ≈ 7 events may happen in the region within a few years.  相似文献   

11.
主要研究2009年7月24日西藏尼玛西南MS5.6地震的基本参数、地震序列特征、震源参数、发震构造等;利用震中附近600km范围内台站测定参数研究地震的震源机制解,与哈佛大学给出的震源机制解较一致,且与通过现场考察的发震断层走向具有一致性。研究认为本次地震发生在冈底斯山—拉萨块体内部,断裂为NNW向,主要受张应力作用产生左旋走滑正断层活动。此外还分析了震前地震学条带异常特征,结束表明,震前1年出现NW向条带非常显著,研究结论为该地区今后地震预测提供科学依据。  相似文献   

12.
The paper presents results of studying stresses and seismicity of the lithosphere in the Baikal rift zone at the present (instrumental) stage of its evolution. These results are well consistent with the theory of self-organization of complex dynamic systems and can be used for the classification of certain features and properties of the Baikal rift seismogenic system studied. Application of the theory of nonlinear dynamic systems to the analysis of stresses and seismicity allowed us to develop a concept of a complex spatiotemporal structure of the stress state of the lithosphere and seismicity in the region. In terms of this concept, the distribution of strong earthquakes in time is explained in terms of bifurcations (catastrophes) of stresses in the rift zone. Extrapolation of the results indicates that a stress catastrophe in lithosphere of the rift zone can take place in the next few years years, which increases the probability of occurrence of strong (M ≈ 7) earthquakes in the Baikal region. A model with bifurcation of triple equilibrium most consistent with the phase image of regional stresses is proposed as a scenario of the stress state evolution in the lithosphere of the Baikal rift zone.  相似文献   

13.
Some characteristics of the seismic regime of the Baikal rift zone for the analogue (1960–2000) and digital (2001–2006) registration modes are considered. It was ascertained that the general number of seismic events recorded by digital equipment increased by two times in comparison with the analogue observation period and the catalog completeness level was lowered to K P = 7.0 as well. The focal mechanisms of 110 earth-quakes with K P ≥ 8.0 were examined. The overwhelming majority of them during 2001–2006 were due to normal faulting and normal faulting with strike-slip components. Special attention was given to study of the strong events (K P ≥ 13.5 and MPSP ≥ 4.7), whose focal solutions reveal the regional stress field.  相似文献   

14.
The Hsingtai, China earthquakes of March 1966 were a series of destructive earthquakes associated with the Shu-lu graben. Five strong shocks of Ms ≥ 6 occurred within a period of less than a month, the largest of which was Ms 7.2. Body and surface waves over the period range from several to 100 s have been modeled for the four largest events using synthetic seismograms in the time domain and spectral analysis in the frequency domain. Data from ground deformation, local geology, regional seismic network, and teleseismic joint epicenter determination have also been used to constrain the source model and the rupture process.The fault mechanism of the Hsingtai sequence was mainly strike-slip with a small component of normal dip-slip. The strikes of the four largest shocks range from ～ N26° to 30°E, approximately along strike of the major faults of the Shu-lu graben and the aftershock distribution. The source mechanisms can be explained with a NNW-SSE extensional stress and a NEE-SWW compressional stress acting in the area. The major shocks all had focal depths ～ 10 km.The four largest shocks in the sequence were characterized by a relatively simple and smooth dislocation time history. The durations of the far-field source time functions ranged from 3.5 to 5 s, while the rise times were all ～ 1 s. The seismic moments of the four largest earthquakes ranged from 1.43 × 1025 to 1.51 × 1026 dyne cm?1. The fault sizes of the four events were very close. Assuming circular faults, the diameters of the four events were determined to be between 10 and 14 km. Stress drops varied from ～ 52 to 194 bars. A trend of increasing stress drop with earthquake size was observed.A survey of stress drop determinations for 15 major intraplate earthquakes shows that on the average the magnitude of stress drop of oceanic intraplate earthquakes and passive continental margin events is higher (～ 200 to several hundred bars) than that of continental intraplate earthquakes (～ 100 bars or less).  相似文献   

15.
Estimation and comparison of the energy of seismotectonic deformations in the lithosphere of the Baikal Rift Zone (BRZ) based on observations of large (M ≥ 6) earthquakes for the period of instrumental recording (1950–2002), for a historical period lasting 210 years (1740–1949), and inferred from palaeo-seismological materials for the past 2000 years, all indicate that the hypothesis of a stationary seismic process is appropriate for the region. The locations of maxima of the density of seismotectonic strain energy released during the time intervals under investigation show that most of the failures in the lithosphere occurred approximately in the same areas, which may be interpreted as stress concentrators. The isolines of increased density for the energy of seismotectonic deformations align themselves along the rift features from southwest to northeast in the Baikal region and this allows one to treat the BRZ lithosphere as an extended zone of enhanced, inhomogeneous, energy release of endogenous geotectonic processes. We assessed the power of the seismotectonic processes that reflect the release of endogenous energy through earthquakes. Identification of areas with deficits in the energy of seismotectonic deformations (“energy gaps”) is an important step toward long-term solution of seismic-safety problems for the Baikal region.  相似文献   

16.
The research of the information dimension (D 1) in an active fault zone considers the contribution of each seismic event to information and reflects the characteristics of the temporal and spatial distributions of earthquakes from a new point of view, avoiding some short-comings of the research about the capacity dimension (D 0). The results of calculation show that the information dimension of the temporal distribution in Xianshuihe active fault zone before Luhuo large earthquake isD 1=0.1051. It is a consult creterion of large earthquakes in future in the fault zone. The information dimensions of the temporal distribution of the earthquakes in Anninghe active fault zone are respectivelyD 1(t N)=0.1363 (for the north section) andD 1(t S)=0.06710 (for the south section). The information dimensions of the spatial distribution are respectivelyD 1(K N)=1.053 (for the north section) andD 1(K S)=0.7758 (for the south section). The north section and the south section belong to two self-similar systems with different information dimensions respectively. The extent of the self-organization of seismic activity in the south section is higher than that in the north section. This is helpful for us to judge the major dangerous section in the key region of the seismic monitoring. The research about the information dimension of the temporal and the spatial distributions of earthquakes is significant for the exploration of active fault zones and seismic prediction.  相似文献   

17.
This paper introduces the basic parameters, focal mechanism solutions and earthquake sequence characteristics of the Kalpin MS5.3 earthquake sequence of December 1, 2013, and analyzed seismic activity before the earthquake, the adjacent tectonic features and the precursory anomaly at fixed points within a range of 200km. Research indicates:(1) The earthquake occurred on Kalpin fault, the source rupture type is thrust faulting with sinistral strike-slip component. (2) The earthquake sequence is mainshock-aftershock type, with the aftershock distribution attenuating quickly and trending NE. (3) Abnormal seismic activity before the earthquake was characterized by seismically nesting quiescence of MS2.0-4.0 earthquakes, seismic quiescence of MS4.0 earthquakes and seismic belts of MS3.0 earthquakes in the Kalpin block, abnormal enhancement zone of moderate earthquakes on Puchang fault and seismological parameters. (4) Anomalies of precursory observation data at fixed stations are mainly characterized by mutation. Apart from the borehole tiltmeter in Halajun, the spatial distribution of other abnormal precursors showed a phenomenon of migration from the near field to far field and from the epicenter to the peripheries.  相似文献   

18.
Data on the time moments and numbers of weak earthquakes (M ≥ 0) are analyzed in five regions of Central Asia where long-term extensive instrumental observations of seismicity were conducted. Spectra of time moments of seismic events were calculated in the range of periods from 1 to 48 h with a step of half an hour. The time variations in the numbers of these earthquakes were also calculated in windows of 4 to 48 h wide with a summation step of 1 h. The presence of significant high-quality spectral extrema at periods of 24 and 12 h is established for all catalogs used, and less significant extrema at a period of 8 h are established for some catalogs. These periodicities are observed in the analysis of weak earthquakes with M < 2.2 (K < 8) and are virtually absent for stronger seismic events. It is shown that lunisolar tides have no appreciable gravitational effect on the observed variations in seismic emission. Daily variations in the actual sensitivity of the observation network due to the daytime increase in the noise level as a factor responsible for the observed diurnal periodicity raise doubts.  相似文献   

19.
—?Plans for a hydroacoustic network intended to monitor compliance with the CTBT call for the inclusion of five T-phase stations situated at optimal locations for the detection of seismic phases converted from ocean-borne T phases. We examine factors affecting the sensitivity of land-based stations to the seismic T phase. The acoustic to seismic coupling phenomenon is described by upslope propagation of an acoustic ray impinging at a sloping elastic wedge. We examine acoustic to seismic coupling characteristics for two cases; the first in which the shear velocity of the bottom is greater than the compressional velocity of the fluid (i.e., v p > v s > v w ), the second is a weakly elastic solid in which v s << v w < v p . The former is representative of velocities in solid rock, which might be encountered at volcanic islands; the latter is representative of marine sediments. For the case where v s > v w , we show that acoustic energy couples primarily to shear wave energy, except at very high slope angles. We show that the weakly elastic solid (i.e., v s << v w ) behaves nearly like a fluid bottom, with acoustic energy coupling to both P and S waves even at low slope angles.¶We examine converted T-wave arrivals at northern California seismic stations for two event clusters; one a series of earthquakes near the Hawaiian Islands, the other a series of nuclear tests conducted near the Tuamoto archipelago. Each cluster yielded characteristic arrivals at each station which were consistent from event to event within a cluster, but differed between clusters. The seismic T-phases consisted of both P- and S-wave arrivals, consistent with the conversion of acoustic to seismic energy at a gently sloping sediment-covered seafloor. In general, the amplitudes of the seismic T phases were highest for stations nearest the continental slope, where seafloor slopes are greatest, however noise levels decrease rapidly with increasing distance from the coastline, so that T-wave arrivals were observable at distances reaching several hundred kilometers from the coast. Signal-to-noise levels at the seismic stations are lower over the entire frequency spectrum than at the Pt. Sur hydrophone nearby, and decrease more rapidly with increasing frequency, particularly for stations furthest from the continental slope.  相似文献   

20.
The forward and inverse problems of studying crustal stress state from breakout data of inclined boreholes are concisely stated. Direction of the maximum horizontal principal stress (compressive) and relative magnitudes of the horizontal stresses to the vertical stress in the upper crust in two regions of the Jizhong depression, the North of China, are obtained by analyzing the breakout data of 6 inclined wells. To get stable results in the analysis we searched for the unknown parameters both forwardly and inversely. The results show that the maximum azimuths of the horizontal principal compressive stresses in the central and southern part of the Jizhong depression are N86°E and N77°E, respectively, while the relative magnitudes of the three principal stresses in the upper crust (about 1000–4000 m) of the depression are variable. In the central part of the Jizhong depression we have foundS H :S V :S h =1.38:1.00:0.57, whereS H ,S V andS h are the maximum horizontal, vertical and minimum horizontal stress, respectively. This indicates that the present stress regime in this area is of strike-slip faulting type. In the southern part of the depression we have obtainedS H :S V :S h =0.80:1.00:0.62, indicating a normal faulting stress regime in the shallow part of the crust.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号