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1.
The seismicity associated with the convergence of the Indian and Eurasian plates, from 1964 to August 1990 was scanned using the M8 algorithm with a view to identify the times of increased probabilities (TIPs) of the earthquakes of magnitudes greater or equal to 6·4 that occurred during the period from 1970 to August 1990. 23 out of 28 earthquakes (M ? 6·4) have been predicted. These were preceded by specific activation of the earthquake flow which was picked up by the M8 algorithm. The earthquake of August 1988 in the Himalaya could not be predicted, the other four unpredictable earthquakes occurred in the early dates of the catalogue (1970–1971) and hence their TIPs could not be diagnosed. Two current alarms are diagnosed, one in the Indo-Burmese arc and the other in the Hindukush-Pamir region. The algorithm provides the correlation between the earthquakes and their area of activation (both in time as well as in space) which, when compared with the local geology, may help to comment on the present day status of the seismic features on the surface.  相似文献   

2.
由于受到台站分布不理想、速度结构研究不准确以及震相拾取误差等因素的影响,常规地震定位结果精度较低。因此,研究收集了辽宁省地震台网的地震目录及震相数据,采用双差地震定位方法,对海城及其附近地区（39°N-43°N,120°E-126°E）20 a的1 400多次地震进行重新定位。与原始定位结果相比,双差定位结果表明：1）震中更加呈条带状集中,尤其在40.5°N-41.0°N,122.0°E-123.0°E区间,与该地区的海城河-大洋河断裂带走向相一致;2）该地区地震多发生于地下5~20 km,与该区中地壳存在的低速高导层相对应;3）深度剖面图显示,大部分地震沿垂直向下柱状分布,原因是该处有粉碎性破裂带,从地下25 km处延伸到近地表。双差定位算法使得定位后均方根残差的平均值由0.74 s下降到0.26 s。辽宁地区的地震震级与发生地震数量有关,地震数量陡然增多,大地震发生概率增大。  相似文献   

3.
Earthquake activity is monitored in real time at the Koyna reservoir in western India, beginning from August 2005 and successful short term forecasts have been made of M ∼ 4 earthquakes. The basis of these forecasts is the observation of nucleation that precedes such earthquakes. Here we report that a total of 29 earthquakes in the magnitude range of 3.5 to 5.1 occurred in the region during the period of August 2005 through May 2010. These earthquakes could broadly be put in three zones. Zone-A has been most active accounting for 18 earthquakes, while 5 earthquakes in Zone-B and 6 in Zone-C have occurred. Earthquakes in Zone-A are preceded by well defined nucleation, while it is not the case with zones B and C. This indicates the complexity of the earthquakes processes and the fact that even in a small seismically active area of only 20 km × 30 km earthquake forecast is difficult.  相似文献   

4.
Seismicity of the Himalayan arc lying within the limits shown in figure 1 and covering the period 1964 to 1987 was scanned using M8 algorithm with a view to identifying the times of increased probabilities (TIPs) of the occurrence of earthquakes of magnitude greater than or equal to 7·0, during the period 1970 to 1987. In this period, TIPs occupy 18% of the space time considered. One of these precedes the only earthquake in this magnitude range which occurred during the period. Two numerical parameters used in the algorithm, namely the magnitude thresholds, had to be altered for the present study owing to incomplete data. Further monitoring of TIPs is however warranted, both for testing the predictive capability of this algorithm in the Himalayan region and for creating a base for the search of short-term precursors.  相似文献   

5.
Koyna-Warna region of western India is an active seismic zone due to the Reservoir Triggered Seismicity (RTS). Earthquake precursor studies are carried out monitoring hydrochemical and stable isotope signatures in the groundwater from 15 bore wells since January 2005, for more than 12 years (January 2005 to February 2017). Depth of these boreholes ranges from 100 to 250 m. Cyclic or temporal variation in hydrochemistry is observed in few sensitive wells in Koyna region. The Govare well in Koyna is found to be most sensitive and the observed hydrochemical cycle is closely associated with local earthquakes of M > 5. The earthquakes M <5 occurring either in Warna cluster or close to the observation wells, did not generate hydrochemical precursory changes. The increase in hydrochemistry is hypothesized as mixing of two aquifer waters with different hydrochemistry. It is noted that a precursory hydrochemical cycle is observed during first quarter of 2015, but no earthquake M > 5.0 occurred till date. The cyclic changes in hydrochemistry, however, indicate on-going earthquake processes and an impending earthquake of M > 5 in the region.  相似文献   

6.
Hourly monitoring of electrical conductivity (EC) of groundwater along with groundwater levels in the 210 m deep boreholes (specially drilled for pore pressure/earthquake studies) and soil Rn gas at 60 cm below ground level in real time, in the Koyna-Warna region (characterized by basaltic rocks, >1500 m thick, and dotted with several sets of fault systems), western India, provided strong precursory signatures in response to two earthquakes (M 4.7 on 14/11/09, and M 5.1 on 12/12/09) that occurred in the study region. The EC measured in Govare well water showed precursory perturbations about 40 h prior to the M 5.1 earthquake and continued further for about 20 h after the earthquake. In response to the M 4.7 earthquake, there were EC perturbations 8 days after the earthquake. In another well (Koyna) which is located 4 km north of Govare well, no precursory signatures were found for the M 4.7 earthquake, while for M 5.1 earthquake, post-seismic precursors were found 18 days after the earthquake. Increased porosity and reduced pressure head accompanied by mixing of a freshwater component from the top zone due to earthquakes are the suggested mechanisms responsible for the observed anomalies in EC. Another parameter, soil Rn gas showed relatively proportional strength signals corresponding to these two earthquakes. In both the cases, the pre-seismic increase in Rn concentration started about 20 days in advance. The co-seismic drop in Rn levels was less by 30% from its peak value for the M 4.7 earthquake and 50% for the M 5.1 earthquake. The Rn anomalies are attributed to the opening and closing of micro-fractures before and during the earthquake. On line monitoring of these two parameters may be useful to check the entire chemistry change due to earthquake which may help to forecast impending earthquakes.  相似文献   

7.
Eyidogan  Nalbant  Barka  & King 《地学学报》1999,11(1):38-44
The 1924 Pasinler & 1983 Horasan-Narman earthquakes which struck the Erzurum region occurred on the NE–SW-trending Horasan fault zone about 60 km east of Erzurum basin. The inversion of teleseismic seismograms, the aftershock pattern and the surface faulting of the 30 October 1983 ( M s = 6.8) Horasan-Narman earthquake indicate that it had dominantly left-lateral motion. One moderately sized aftershock occurred 8 h after the main event and two others a year later on the NE extension of the fault zone. The aftershock distribution dominantly overlapped with the Horasan fault zone, and the aftershocks also migrated from south-west to north-east within the year following the mainshock. The results obtained from modelling of static stress changes caused by the 1983 earthquake are consistent with the spatial distribution of aftershocks. Macroseismic observations of the 1924 earthquake ( M s = 6.8) indicated that this event occurred on the SW extension of the Horasan fault zone. Static stress modelling of the 1924 earthquake, by using the same input parameters of the 1983 event, has shown that its occurrence increased the stress in the region of the 1983 rupture zone. The static stress changes caused both by the 1924 and the 1983 earthquakes has increased the failure stress at the NE and SW extensions of the Horasan fault zone and in Narman area. Furthermore, the stress has decreased in the vicinity of the Erzurum fault zone, east of the city of Erzurum, the largest city in eastern Turkey, and in the populated Sarikamis area. This might delay the occurrence of a future probable damaging earthquake in these areas.  相似文献   

8.
The northern Tien Shan is the northern front of the Himalayan mountain belt, which resulted from the collision between the Indian and Eurasian Plates. This region encompasses the most active seismic zones of the orogen, which generated the strongest (M > 8) earthquakes. Since there are scarcely any written accounts, the only way to trace back strong earthquakes is the paleoseismologic method. Since 1984 we have been studying the northwestern Issyk Kul’ basin, where there are differently directed anticlines, which constitute the Kungei meganticline. Here, several active tectonic structures (faults, folds) are located, whose development was accompanied by strong earthquakes. Our field studies of 2008 in the Iiri-Taldybulak Valley, along the adyrs (foothills) of the Kungei-Ala-Too Range, revealed two unknown historical earthquakes. The first one, which occurred along the southern rupture in the late 7th century A.D., gave rise to a seismic scarp; the latter broke through the river floodplain and a tash-koro (ancient settlement). The second one, which occurred along the northern rupture in the late 9th century A.D., increased the height of the seismic scarp, existing on the Early Holocene and older terraces. Note that this region already records a strong seismic event around 500 A.D. Archeologic data have revealed one more strong earthquake, which took place in the 14th century A.D. Note that the above-mentioned strong seismic events are coeval with the decline of the nomadic cultures (Wusun, Turkic, Mogul) in the northern Tien Shan and Zhetysu (Semirech’e).  相似文献   

9.
震级-频度分布（FMD）是地震学研究中最重要的经验公式之一,相关系数b是构造学和地震危险性评估的重要因子,具有表征前震和余震的特性。辽宁省地震多发生在金州断裂附近,自1975年海城7.3级地震发生后,与金州断裂交汇的海城河—大洋河断裂开启活跃模式,其东南端岫岩附近在1999年又发生5.6级地震。近年来盖州附近地震活动也在增强。因此,本文利用b值空间分布特征对海城及其邻区的应力分布特点进行研究。震源定位准确与否直接影响b值计算,双差定位后的数据与常规目录相比具有更高的精度,但是完整性有一定下降。本文收集了中国地震台网1981—2005年的辽宁省地震目录,并进行双差定位,比较分析了常规目录数据和双差数据的b值分布差异,认为在地震密集区,双差定位后的数据可以被用来获得更准确的b值。对主要研究区进行网格划分,使用双差数据,得到b值的水平和垂直分布特征。结果表明：b值为0.6~1.8,随深度增加而降低;岫岩和盖州震区具有较低的b值,意味着具有较高的地震危险性;浑河震区与海城河—大洋河断裂东南方向具有较高的b值,说明该区域未来发生大地震的概率很低;与金州断裂交汇区域的b值在1.0附近,说明该地区应力暂时处于稳定状态,未来具有较低的地震危险性。  相似文献   

10.
Water level fluctuations in twenty-one observation wells have been monitored for the last 10 years around the seismically active Koyna–Warna region, western India where earthquakes continue to occur even after four decades of the initiation of the seismic activity in the region. Fourteen of the observation wells act as volume strain meters as their water levels show earth tidal signals. Our analysis suggests three types of response of the well water levels to seismo-tectonic effects, i) one to local earthquakes, ii) to regional and teleseismic events, and iii) to local fluctuations in rock strain on regional scale. We observed five cases of co-seismic step-like well water level changes, of the order of few centimeters in amplitude, related to earthquakes in the magnitude range 4.3 ≤ M ≤ 5.2. All these earthquakes occurred within the network of wells drilled for the study and within 25 km distance of the recording wells. In three cases, drop in well levels preceded co-seismic step-like increases, which may be of premonitory nature. The second type of response is observed to be due to the passing of seismic waves from regional and teleseismic earthquakes like the M 7.7 Bhuj event on January 26, 2001 and the M 9.3 December 26, 2004 Sumatra earthquake. The third type is a well level anomaly of centimeter amplitude coherently occurring in several wells. The anomalies are similar in shape and last for several hours to days.From our studies we conclude that the wells in the network appear to respond to regional strain variations and transient changes due to distant earthquakes. The two factors which are important to co-seismic steps due to local earthquakes are the magnitude and epicentral distance. From the limited number of events we found that all local earthquakes exceeding M ≥ 4.3 have produced co-seismic changes. No such changes were observed for earthquakes below this magnitude threshold.  相似文献   

11.
An analysis of the data in the catalogues of Italian earthquakes indicates that large earthquakes which occur in the area of radius of about 140 km centered in the Straits of Messina occur in sequences. Each sequence is generally formed by two events and covers an average time window of 10 years.The last four sequences occurred in the time windows 1783–1891, 1818–1823, 1865–1870, 1905–1908 and are separated by about 40 years indicating that in that area there is now a gap in the time domain.The analysis of the data in the Catalogue for the region between the latitudes 39°N and 41°50′N indicates that in that region the large earthquakes occurred in 13 sequences. Each sequence is formed by 3 events in average and covers an average time window of 7 years. This indicates that, after the earthquake of Nov. 1980, which occurred after a gap of 67 years, other moderately large earthquakes may be expected in that area in the next few years.  相似文献   

12.
An attempt has been undertaken to examine time series of volcanic and seismic events in a multidimensional reference system related to the parameters of the Earth’s orbital motion. Volcanic eruptions and strong (M > 5) earthquakes (a sample from the USGS/NEIC seismological database: Significant Worldwide Earthquakes) [18] were analyzed within the fields of the JPL Planetary and Lunar Ephemerides, (DE-406) astronomical indicators [19]: the Earth-Moon distance, Earth-Sun distance, ecliptic latitude of the Moon, and the differences between the geocentric longitudes of the Moon and Sun, Venus and Sun, and Mars and Sun. Distribution spectra were obtained and normalization was performed taking the nonuniform motion of celestial bodies into consideration, and the values of multidimensional diurnal probability were calculated. As a result, the statistically reliable drift in the distribution of geoevents was calculated relative to the duration of the intervals of multidimensional diurnal probability, which indicates distribution regions where more geoevents can take place during shorter intervals (and vice versa). Linear relationships between the multidimensional diurnal probability and diurnal probability of geoevents were found. All these results and the astronomic ephemerides were used as a base for computing the probabilities of volcanic and seismic activity of the Earth for the period of 2005–2007. The spatial structure of volcanic and seismic processes was examined, which allowed the revelation of probabilistic parameters of the spatiotemporal structure of Earth’s geodynamic activity and outlining an approximate algorithm for its monitoring.  相似文献   

13.
Variations of seismic mode in the region of the Avachinsky Gulf (Kamchatka, Russia) are considered. Observed anomalies (seismic quiescence, the ring seismicity, reduction of the slope of the earthquake recurrence diagram) provide a basis to consider this region as a place of strong earthquake preparation. The Kamchatka regional catalogues of earthquakes between 1962–1995 were used in the analysis. A reduced seismicity rate is observed during 10 years in an area of 150 km × 60 km in size. During the last five years, in the vicinity of the area considered, earthquakes with M > 5 occurred three times more often than the average over thirty years. It is interpreted as ring seismicity. The block of 220 km × 220~km in size, including the quiescence zone, is characterized by a continuous decrease of the recurrence diagram slope, which has reached a minimum value for the last 33 years in this region.  相似文献   

14.
The earthquakes with magnitude M 6 which occurred in North China (30°–42°N, 105°–124°E) from 780 B.C. to 1978 A.D. have been analysed. Most of them appear in groups, each of which is confined to a definite region and period of time, called respectively the active region and active period. From 780 B.C. to 1000 A.D., groupings of earthquakes were not apparent, due to scanty data. Since 1000 A.D., 16 groups of earthquakes can be recognized. Statistics show that about 73% of the earthquakes occurred in groups. This implies that grouping of earthquakes of M 6 is a characteristic feature of seismic activity in North China. On this basis, a concept of a unified seismogenic process of major earthquakes has been proposed with the support of the geodetic data. Finally, the significance of this concept with regards to earthquake prediction has been discussed.  相似文献   

15.
The role of the lateral structure of the lithospheric mantle in the seismotectonics and seismicity of the southern part of the Russian Far East has been investigated. The positions of the epicenters of all the major earthquakes in Sakhalin (M ≥ 6.0), as well as in the Amur region and the Primorye zones (M ≥ 5.0), are defined by the boundaries of the Anyui block of highly ferruginous mantle, which lies at the base of the Sikhote-Alin area. Three cycles of large earthquakes are recognized in the region: the end of the 19th-beginning of the 20th century, the mid-20th century, and end of the 20th-beginning of the 21st century. In the seismic zone of the Amur region (hereafter, the Amur seismic zone), the epicenters of the large earthquakes in each cycle migrate from the SW to NE along the Tan-Lu fault megasystem at a rate of 30–60 km/yr. The specific features of the seismicity of the region are explained by the repeated arrival of strain waves from the west. The waves propagate in the upper part of the mantle and provoke the activation of the deep structure of the region. The detailed analysis of the earthquakes in the Sikhote-Alin area (M ≥ 4.0) in 1973–2009 confirmed the clockwise tectonic rotation of the mantle block. The characteristics of the Primorye zone of deep-focus seismicity at the Russia-China boundary are stated. Since 1973, 13 earthquakes with M ≥ 6.0 have been recorded in the zone at a depth of 300–500 km. This number of earthquakes is at least twice as many as the number of large deep-focus earthquakes elsewhere in the Sea of Japan-Sea of Okhotsk transition zone. The unique genesis of the Primorye seismic zone is related to the additional compression in the seismofocal area due to the creeping of the Anyui mantle block onto the subduction zone during its rotation. The geodynamic implications of the seismotectonic analysis are examined, and the necessity of division of the Amur plate into three geodynamically independent lithospheric blocks is substantiated.  相似文献   

16.
A three-component broadband seismograph is in operation since January 2007 at the Indian School of Mines (ISM) campus. We have used the broadband seismograms of two local earthquakes M <3 recorded by this single station to illustrate its efficacy in understanding the source processes and tectonics in Dhanbad area. Source parameters and fault plane solutions are obtained through waveform inversion. It is observed that these two earthquakes occurred in the lower crust at a depth of 26 km by strike slip faulting. North-south compressional and east-west tensional stresses are dominant in the area, and the lower crust is the source area for the local earthquakes.  相似文献   

17.
Following the December 2004 and March 2005 major shallow foci inter-plate earthquakes in the north Sumatra region, a slab-tear fault located within the subducting Indian plate ruptured across the West Sunda Trench (WST) within the marginal intra-plate region. Trend, length and movement pattern of this New Tear Fault (NTF) segment is almost identical to another such slab-tear fault mapped previously by Hamilton (1979), located around 160 km south of NTF. Seismic activity along the NTF remained quasi-stable till the end of the year 2011, when an earthquake of magnitude 7.2 occurred on 10.01.2012 just at the tip of NTF, only around ～100 km within the intra-plate domain west of WST. The NTF rupture propagated further towards SSW with the generation of two more large earthquakes on 11.04.2012. The foreshock (10.01.12; M7.2) — mainshock (11.04.12; M 8.6) — aftershock (11.04.12; M 8.2) sequence along with numerous smaller magnitude aftershocks unmistakably define the extension of NTF, a slab-tear fault that results tectonic segmentation of the convergent plate margin. Within the intra-plate domain most earthquakes display consistent left-lateral strike slip mechanism along NNE trending fault plane.  相似文献   

18.
Research for evaluation of geologic hazards involving earthquakes and volcanic eruptions in southern Argentina seems to have historically received little attention. Nevertheless, the relatively small work done indicates a Neogene tectonic architecture in the area with capability of generating potential hazardous earthquakes in a growing population region. Seismicity and some morphotectonic evidences of Quaternary activity of the Magallanes–Fagnano left‐lateral fault system in the transform boundary between South America and Scotia plates, are analysed in this paper. This fault system is considered to be an important seismogenic source, responsible for large earthquakes that have occurred in southern Argentina. Some examples from the South and Austral Andean Volcanic Zones are also examined in order to show recent volcanic activity which also generated crustal seismicity. Preliminary hazard estimation clearly shows the presence of both potentially active volcanic centres in southern Patagonia that may also trigger seismicity and the high probability for large crustal earthquake generation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

19.
Frequency-size relation of earthquakes in a region can be approximated by the Gutenberg-Richter law(GR). This power-law model involves two parameters: a-value measuring seismic activity or earthquake productivity, and b-value describing the relation between frequencies of small and large earthquakes.The spatial and temporal variations of these two parameters, especially the b-value, have been substantially investigated. For example, it has been shown that b-value depends inversely on differential stress. The b-value has also been utilized as earthquake precursor in large earthquake prediction.However, the physical meaning and properties of b-value including its value range still remain as an open fundamental question. We explore the property of b-value from frequency-size GR model in a new form which relates average energy release and probability of large earthquakes. Based on this new form of GR relation the b-value can be related to the singularity index(1-2/3 b) of fractal energy-probability power-law model. This model as applied to the global database of earthquakes with size M ≥ 5 from 1964 to 2015 indicates a systematic increase of singularity from earthquakes occurring on mid-ocean ridges, to those in subduction zones and in collision zones.  相似文献   

20.
The Nurek Reservoir is located in an area of high seismicity. An average of 5–6 earthquakes of (Russian energy class)K = 10 and 1–2 earthquakes ofK = 11 per year occurred in the vicinity of the reservoir. The largest local earthquake recorded fell in the energy classK = 14 (1956).

At the end of 1972, after the water level had risen to 100 m, earthquake activity increased sharply. Three events ofK = 12 were recorded during one month and the total number of earthquakes (K 7) exceeded three times the former mean level of seismicity.

Spatial and temporal properties in the epicentral distribution showed a migration from the southwest toward the reservoir.

Earthquake mechanisms of 215 events ofK 9 since 1960 were analysed. Fault plane solutions for some of the earthquakes which occurred after the impoundment were found to be different from the ordinary ones.  相似文献   


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