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1.
The frequency dependence of the function of the seismic wave attenuation was determined for the first time for southern Sakhalin on the basis of seismic coda of local earthquakes using the model of single scattering. The algorithm of the automated definition of the scalar seismic moments was realized for small earthquake foci. Mass estimates of the scalar seismic moments were obtained as exemplified by the after-shocks of the August 17, 2006, Gornozavodsk earthquake (MW 5.6) and the May–June 2004 Kostromskoe earthquake swarm events, which occurred in South Sakhalin. The dynamic parameters of the earthquake foci were determined from the SH-wave spectra adjusted for absorption and geometrical spreading. The loglinear relationship determined between the seismic moment and the local magnitude is in good agreement with the estimates obtained for other regions and, in a certain sense, does not contradict the average world dependence.  相似文献   

2.
A catalogue of aftershocks of the 2007 Nevelsk earthquake (M w = 6.2) was prepared on the basis of the data from the local network of digital seismic stations established on the southern part of Sakhalin Island. The parameters of the aftershock hypocenters were determined using the method of the seismic wave travel time inversion. The errors in the determination of the coordinates of the seismic events were analyzed. The particularities of the spatiotemporal distribution of the aftershocks in the source zone of the earthquake were established. It was shown that a strong aftershock was a subsource earthquake with its own source zone. This explains the disagreement between the energetic characteristics and the size of the aftershock zone of the Nevelsk earthquake.  相似文献   

3.
The August 17 (18), 2006, Gornozavodsk earthquake (Mw = 5.6) in the southwestern part of Sakhalin was preceded by a number of anomalous seismological and geophysical phenomena. The extensive data recorded by a network of digital seismic stations make it possible to track the aftershock dynamics of the process within 24 hours after the main event. The paper describes various manifestations of the earthquake.  相似文献   

4.
The results of the instrumental and macroseismic studies are reported for the tangible earthquake with intensity of up to 5–6 and amplitude of MLH = 4.8 that occurred near the western coast of Sakhalin Island. The main parameters of the Kostromskoe earthquake have been estimated in two versions: (1) based on the data from the local network of digital stations located in southern Sakhalin, and (2) from the complex of local, regional, and global observations. It has been noted that the development of the local network in southern Sakhalin allowed the seismic regime in the earthquake area to be investigated in more detail and the mechanisms of both the individual weak and group events to be derived. The acquired data on the dislocation style of the main shock and aftershocks in the days following the event were used for the geological-tectonic interpretation of the Kostromskoe earthquake.  相似文献   

5.
This paper reports the results of field observation and the study of coastal tectonic deformations related to the Nevelsk tsunamigenic earthquake (August 2, 2007, M ～ 6.1) obtained in August-September of 2007. The earthquake caused a 0.5- to 1.5-m rise of and partial desiccation of the southern, central, and northern benches and the formation of longitudinal structural ridges seaward of Lovetskaya Bay. In the framework of the new model of the Kamyshovy (West Sakhalin) Anticlinorum as a structure of the Quaternary and Middle Quaternary crustal detachment, the relationships between the earthquake and the slow gravitational creep of the upper crust on its western slope with local squeezing of the Middle Miocene Nevelsk siltstones are discussed.  相似文献   

6.
Detailed seismic zoning of Sakhalin based on seismological, tectonic, geomorphological, hydrogeological, and other data is discussed. It is shown that strong crustal earthquakes occurred at the boundary between the Eurasian and Okhotsk plates and their recurrence in Central Sakhalin is equal to the duration of the tectonic cycle (75 years). This boundary in North Sakhalin is marked by the Upper-Piltun fault, which was the epicenter of the 1995 Neftegorsk earthquake with an intensity of 9. The analysis of paleosoils in the fault zone showed that such events repeat with an interval of 400 years. The development of large oil and gas reservoirs on the Sakhalin shelf will be accompanied by intensification of the seismicity, which can reach a magnitude of M = 6.0–6.5 in the Lunskoye field.  相似文献   

7.
The results of deep seismic profiling through Southern Sakhalin, the southern Sea of Okhotsk, and the Southern Kuril Islands allowed the identification of deep fault zones, the hypocenter locations, the features of the stress state, and the types of seismic dislocations at the earthquake sources. The east side of the fault was upthrown relative to the west side beneath the southern part of the Tatar Strait and Sakhalin Island and led, as a result of multiple thrusting events along the fault over the geologic history, to the rise and 5-8 km displacement of the seismic boundaries. The true uplift of the Greater Kuril arc block was determined using the focal mechanism solutions. The seismoctectonics and present-day dynamics of the crustal blocks were estimated using a detailed joint analysis of the position of the structural boundaries at the seismic section and the seismotectonic movements according to the earthquake focal mechanisms.  相似文献   

8.
The seismic anisotropy of the mantle is studied based on the data of S and ScS waves from earthquakes occurred in the mantle transition zone over the period of 2007–2013 and recorded by seismic stations in the continental margin of Asia, on Sakhalin Island, and in the southern part of the Kamchatka Peninsula. The measurements of the azimuths of polarization of the fast S and ScS waves in the continental margin of Asia show that they are predominantly oriented in the E–SE directions. Based on the distribution of the shear wave splitting parameters, the symmetry of the medium can be described in terms of a transversely isotropic model with a horizontal symmetry axis and may correspond to horizontal flow in the upper mantle beneath the Amur Plate. The fast azimuths of polarization of ScS wave, which were determined to be of N–NE directions in the northern area of Sakhalin Island and in the continental part of Asia, may correspond to an inclined flow under the conditions of oblique subduction and complex geometry of the downgoing Pacific Plate. In the south of the Kamchatka Peninsula, the S- and ScS-wave azimuths of polarization from the M 8.4 Sea of Okhotsk earthquake are determined to be oriented along the direction of the Pacific Plate motion. The fast-S-wave azimuths of polarization from the aftershocks of the Sea of Okhotsk earthquake and from other large events of 2008–2009 are determined to be nearly parallel to the motion trend of the Pacific Plate, but orthogonal to it for the events of 2008–2009. On the basis of the distribution of azimuths of polarization of the fast S waves, the symmetry of the medium can be described in terms of a transversely isotropic model with the symmetry axis inclined orthogonally to the plane of downgoing plate and oriented westward orthogonally to the trench strike.  相似文献   

9.
Earthquakes in Kenya are common along the Kenya Rift Valley because of the slow divergent movement of the rift and hydrothermal processes in the geothermal fields. This implies slow but continuous radiation of seismic energy, which relieves stress in the subsurface rocks. On the contrary, the NW-SE trending rift/fault zones such as the Aswa-Nyangia fault zone and the Muglad-Anza-Lamu rift zone are the likely sites of major earthquakes in Kenya and the East African region. These rift/fault zones have been the sites of a number of strong earthquakes in the past such as the M w = 7.2 southern Sudan earthquake of 20 May 1990 and aftershocks of M w = 6.5 and 7.1 on 24 May 1990, the 1937 M s = 6.1 earthquake north of Lake Turkana close to the Kenya-Ethiopian border, and the 1913 M s = 6.0 Turkana earthquake, among others. Source parameters of the 20 May 1990 southern Sudan earthquake show that this earthquake consists of only one event on a fault having strike, dip, and rake of 315°, 84°, and ?3°. The fault plane is characterized by a left-lateral strike slip fault mechanism. The focal depth for this earthquake is 12.1 km, seismic moment M o = 7.65 × 1019 Nm, and moment magnitude, M w = 7.19 (?7.2). The fault rupture started 15 s earlier and lasted for 17 s along a fault plane having dimensions of ?60 km × 40 km. The average fault dislocation is 1.1 m, and the stress drop, ?σ, is 1.63 MPa. The distribution of historical earthquakes (M w ≥ 5) from southern Sudan through central Kenya generally shows a NW-SE alignment of epicenters. On a local scale in Kenya, the NW–SE alignment of epicenters is characterized by earthquakes of local magnitude M l ≤ 4.0, except the 1928 Subukia earthquake (M s = 6.9) in central Kenya. This NW–SE alignment of epicenters is consistent with the trend of the Aswa-Nyangia Fault Zone, from southern Sudan through central Kenya and further southwards into the Indian Ocean. We therefore conclude that the NW–SE trending rift/fault zones are sites of strong earthquakes likely to pose the greatest earthquake hazard in Kenya and the East African region in general.  相似文献   

10.
Doklady Earth Sciences - The seismotectonic position of the strong earthquake that occurred in the southern part of Sakhalin Island on September 13, 2020, is considered. The maximum shaking...  相似文献   

11.
In this paper the features of seismic process in the southern depression of Lake Baikal are considered. By the data on focal mechanisms of the earthquakes of February 25, 1999 (M w = 6.0), and August 27, 2008 (M w = 6.3), as well as based on configuration of their aftershock fields, it is determined that foci of strong seismic events in southern Baikal are controlled by the greatest structural elements of sublatitudinal and submeridional strikes. It has been shown that a substantial role in the formation of focal zones is played by low-scale destruction of the Earth’s crust, revealed by geological-geophysical data and proved by clustering of seismic shocks. New data on the August 27, 2008, earthquake have proved the high level of seismic danger of this part of the Baikal Rift Zone and allowed us to determine generation conditions of strong earthquakes more precisely.  相似文献   

12.
From the results of high-precision levelling conducted in the southern part of Sakhalin Island, the dynamics of the earth's surface have been determined before the Moneron earthquake in 1971, during its numerous aftershocks and in the following periods. Great subsidence, of up to 7–8 cm, preceded the earthquake, then a 3-year period of steady state followed and at the end of this period the earthquake happened. After this event vertical movements show an inherited character related to the very recent geological structures. Horizontal displacements of the triangulation net, 50 km distant from the earthquake epicentre, were also noted; they had a northeast direction and an amplitude of 7 cm.  相似文献   

13.
Materials of the long- and short-term predictions of the destructive earthquake with the magnitude M LH = 6.6 ± 0.6 within the southwestern shelf of Sakhalin Island are described. The long-term prediction was issued in December 2005 and was affirmed by the Russian Council of Experts on Earthquake Forecasting and Seismic Hazard Assessment in August 2006. The August 17(18), 2006, Gornozavodsk earthquake with a magnitude of M w = 5.6 was the beginning of the realization of this prediction. Six days after its occurrence, the short-term prediction of a much more serious seismic event in the alarm region was prepared. One year later, the prediction of the August 2, 2007, Nevelsk earthquake with a magnitude of M w = 6.2 (M LH = 6.2) proved to be correct.  相似文献   

14.
The satellite radiointerferometry data revealed deformations of the coastal part of Sakhalin Island caused by the earthquake with M w = 6.2 that occurred in the Tatar Strait near Nevelsk. Based on the joint analysis of the satellite and seismological data, dislocation models were contrived for the main shock and its strong aftershocks with the western dip of the fault planes. This made it possible to determine the source mechanisms and the geometrical parameters of the seismic ruptures and to calculate the coseismic vertical and horizontal displacements. In contrast to the one-dimensional model of the insular land displacements determined from the satellite radiointerferometry measurements, this provided a three-dimensional model of the surface deformations for the epicentral zone.  相似文献   

15.
Al-Tarazi  Eid 《Natural Hazards》2000,22(1):17-27
The major earthquake of 22 November 1995, with a moment magnitude MW = 7.1 and a local magnitude ML 6.2, was the beginning of a seismic swarm that occurred in the central part of the Gulf of Aqaba. During this swarm, thousands of earthquakes occurred with local magnitude ranging between 2 and 6.2 from 22 November 1996 to 31 December 1997, when 2089 earthquakes were detected and/or analyzed by the Jordan Seismological Observatory (JSO). The major earthquake strongly affected the near shoreline cities (Figure 1). The maximum observed intensity on these cities was VIII on the modified Mercalli intensity (MMI) scale. A questionnaire was distributed in the main cities of Jordan one week after the major earthquake. The results of this investigation, which demonstrated the observed intensity distribution for Aqaba city, shows a relationship between local conditions, such as geological foundations and topographical characters, and the extent of the destruction. This conclusion was supported by the maximum peak ground acceleration (PGA) measurements inside Aqaba and Eilat cities. From the results of this questionnaire compiled inside Jordan, and other reports and readings compiled from other nearby countries outside Jordan, a preliminary regional iso-intensity map for this major earthquake of 22 November 1995 is presented in this study.  相似文献   

16.
《Applied Geochemistry》1998,13(1):89-94
Radon concentrations were continuously monitored in hot spring water in a 200-m-deep well in the Yugano hot spring area, Izu Peninsula, Japan from July to December 1995. Concentrations of Cl− and SO42− were measured in the hot spring water about once a month from May to December 1995. The Rn concentrations in the hot spring water increased significantly in September and October 1995, when the 1995 earthquake swarm off the E coast of the Izu Peninsula occurred at a distance of about 30 km from the observation well. The 1995 earthquake swarm began on 11 September and became most active from the end of September to the beginning of October. The Rn concentration rose gradually from 8 September, 3 days before the onset of the swarm activity, increasing by about 50% by 17 September. It remained high in October but had returned to normal by the end of November. However, Cl− and SO42− concentrations doubled suddenly from 22 to 23 September and remained high until the end of November. A good correlation between Cl− and SO42− concentrations suggests the same mechanism for their anomalous increases, probably mixing of water with high Cl− and SO42− concentrations caused by crustal deformation related to the seismic swarm activity. However, the anomalous increase in Rn concentration, which began 15 days before these anion increases, cannot be explained by the same water mixing mechanism. A possible mechanism for the anomalous Rn increase is the formation of microcracks caused by compressional stress, which preceded the onset of the earthquake swarm.  相似文献   

17.
The Longquan–Shan fault and the Huya fault are two major neighboring faults of the Longmen–Shan fault zone where the 12 May 2008 Wenchuan earthquake (Mw 7.9) occurred. To study the influence of the Wenchuan event on these two active faults, we calculate changes of Coulomb stress on the Longquan–Shan fault and the Huya fault caused by the Wenchuan mainshock. Our results indicate that the Coulomb stress in the northern section (Zone A) of the Longquan–Shan fault is increased by 0.07–0.10 bars, that in the middle section (Zone B) by 0.04–0.11 bars, and that in the southern section (Zone C) shows almost no change. For the Huya fault, the Coulomb stress is decreased by 0.01–0.03 bars in the northern section (Zone A), 0.10–0.35 bars in the middle section (Zone B), and nearly 0.5 bars in the southern section (Zone C). The epicenter distribution of small earthquakes (ML ⩾ 1.5) on the Longquan–Shan fault and the Huya fault after the Wenchuan earthquake is consistent with the distribution of the Coulomb stress change. This implies that the Wenchuan earthquake may have triggered small events on the Longquan–Shan fault, but inhibited those on the Huya fault. We then use the rate/state friction law to calculate the occurrence probability of future earthquakes in the study region for the next decade. They include the distribution of b-values, magnitude of completeness (Mc), the background seismicity rate, a value of Aσn and the duration for the transient effect (ta) in the study region. We also estimate the earthquake occurrence probabilities on the neighboring faults after the Wenchuan earthquake. Our results show that, the occurrence probability of future earthquakes in the Longquan–Shan has a slight increase, being 7% for M ⩾ 5.0 shocks during the next decade, but the earthquake probability in the Huya region is reduced obviously, being 5–20%, 7–26% and 3–9% for M ⩾ 5.0 shocks during the next decade in sections A, B and C of the Huya fault, respectively.  相似文献   

18.
We performed a probabilistic analysis of earthquake hazard input parameters, NW Turkey covers Gelibolu and Biga Peninsulas, and its vicinity based on four seismic sub-zones. The number of earthquakes with magnitude M ≥ 3.0 occurred in this region for the period between 1912 and 2007 is around 5130. Four seismic source sub-zones were defined with respect to seismotectonic framework, seismicity and fault geometry. The hazard perceptibility characterization was examined for each seismic source zone and for the whole region. The probabilities of earthquake recurrences were obtained by using Poisson statistical distribution models. In order to determine the source zones where strong and destructive earthquakes may occur, distribution maps for a, b and a/b values were calculated. The hazard scaling parameters (generally known as a and b values) in the computed magnitude–frequency relations vary in the intervals 4.28–6.58 and 0.59–1.13, respectively, with a RMS error percentage below 10 %. The lowest b value is computed for sub-zone three indicating the predominance of large earthquakes mostly at Gelibolu (Gallipoli) and north of Biga Peninsula (southern Marmara region), and the highest b value is computed for sub-zone two Edremit Bay (SW Marmara region). According to the analysis of each seismic sub-zone, the greatest risk of earthquake occurrence is determined for the triangle of Gelibolu–Tekirda? western part of Marmara Sea. Earthquake occurrence of the largest magnitude with 7.3 within a 100-year period was determined to be 46 % according to the Poisson distribution, and the estimated recurrence period of years for this region is 50 ± 12. The seismic hazard is pronounced high in the region extending in a NW–SE direction, north of Edremit Bay, west of Saros Bay and Yenice Gönen (southern Marmara region) in the south. High b values are generally calculated at depths of 5–20 km that can be expressed as low seismic energy release and evaluated as the seismogenic zone.  相似文献   

19.
Some 455 events (mb ⩾ 4.5) in the Indo-Myanmar subduction zone are compiled using the ISC/EHB/NEIC catalogues (1964–2011) for a systematic study of seismic precursors, b-value and swarm activity. Temporal variation of b-value is studied using the maximum likelihood method beside CUSUM algorithm. The b-values vary from 0.95 to 1.4 for the deeper (depth ⩾60 km) earthquakes, and from 0.85 to 1.3 for the shallower (depth <60 km) earthquakes. A sudden drop in the b-value, from 1.4 to 0.9, prior to the occurrence of larger earthquake(s) at the deeper depth is observed. It is also noted that the CUSUM gradient reversed before the occurrence of larger earthquakes. We further examined the seismicity pattern for the period 1988–1995 within a radius of 150 km around the epicentre (latitude: 24.96°N; longitude: 95.30°E) of a deeper event M 6.3 of May 6, 1995 in this subduction zone. A precursory swarm during January 1989 to July 1992 and quiescence during August 1992 to April 1995 are identified before this large earthquake. These observations are encouraging to monitor seismic precursors for the deeper events in this subduction zone.  相似文献   

20.
Thermal maturation for the top and base of the Jurassic in the West Siberian megabasin was modeled on the basis of the vitrinite reflectance (Rvt0) data using mathematical modeling and computer simulations. The values of thermal maturation are found to vary within substages PC3-MC32 for the top (or being equivalent to PC3-MC12 on the periphery and southern part of the basin, or to MC2-MC32 in the north) and PC3-AC3 for the base of the Jurassic (or being equivalent to PC3-MC2 on the periphery and southern part of the basin or MC31-AC3 in the north). Thermal maturity levels of the Jurassic in West Siberia are controlled by depths of burial and peak temperatures which the source rocks were subjected to during this period. The situation is further complicated by high heat flows superimposed on the regional background, which are observed in deep fault zones and in the proximity of numerous igneous bodies.  相似文献   

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