Seismic source ruptures of several strong earthquakes of 1989 in Sichuan region of China

We recently proposed a technique able to analyze the trend of the seismic activity by combining neural network model and seismic factors. In this paper, a variation of seismicity was introduced to reflect the corresponding vary of the frequency of earthquake. This variation was used as the precursor of future moderate earthquake. The time intervals of earthquake will be obtained through training the neural network. Then we judge the occurrence of strong earthquakes according to the time intervals. Finally, some statistical researches were made by using the method for the earthquake catalog in Sichuan and Taiwan in China. Through this above, we verify the validity of this method and state the general steps of this method.

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Seismic Source Characteristics of Nine Strong Earthquakes from 1988 to 1990 and Earthquake Activity since 1970 in the Sichuan-Qinghai-Xizang (Tibet) Zone of China

Pure and Applied Geophysics ◽

10.1007/pl00001127 ◽

2000 ◽

Vol 157 (9) ◽

pp. 1423-1443 ◽

Cited By ~ 8

Author(s):

Y. Gao ◽

Z. Wu ◽

Z. Liu ◽

H. Zhou

Keyword(s):

Seismic Source ◽

Earthquake Activity ◽

Strong Earthquakes ◽

Source Characteristics

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TECTONIC POSITION, SISMOLOGICAL AND GEOLOGICAL MANIFESTATION OF 7 SEPTEMBER 2009 ONI?II EARTHQUAKE FOCUS ON THE SOUTHERN SLOPES OF THE GREAT CAUCASUS

Геология и геофизика Юга России ◽

10.23671/vnc.2017.4.9530 ◽

2017 ◽

Author(s):

Е.А. Рогожин

Keyword(s):

Main Shock ◽

Focal Depth ◽

Seismic Source ◽

Epicentral Area ◽

Strong Earthquakes ◽

North East ◽

The North ◽

Tectonic Position ◽

South Slope ◽

Racha Earthquake

В статье приведены сейсмологические и сейсмотектонические материалы о главном толчке и афтершоках Онийского-II землетрясения 7 сентября 2009 г. с Мs = 5,8 на южном склоне Большого Кавказа. Положение облака эпицентров основного толчка и афтершоков совпадает с северной ветвью очаговой зоны Рачинского землетрясения 29.04.1991 г. с МS = 7,0, I0 = 7-8. Глубина гипоцентра основного толчка составляет 8?15 км. В качестве действующей в очаге принята пологая плоскость, погружающаяся в север – северо-восточном направлении. Тип подвижки по такой плоскости – надвиг с компонентами правостороннего сдвига. Сейсмодислокации носили вторичный, гравитационный характер. Результаты палеосейсмологические исследований, проведенных в восточной части эпицентральной области, Рачинского землетрясения, показали, что в этом сейсмической очаге и раньше происходили сильне сейсмические толчки. Согласно полученным данням возраст предыдущего сильного землетрясения в Рача-Джавской зоне (т. е. до 1991 г.) – около 2000 лет назад. Еще одно, болем древнее событие произошло около 6000 лет назад. Период повторяемости сильних землетрясений, подобных катастрофе 1991 г., таким образом, составляет в среднем 2000-3000 лет. The article provides seismological and seismotectonic materials about the main shock and aftershocks of the Oni-II earthquake of 7 September 2009, with MS = 5,8 on the South slope of the Greater Caucasus. The position of the cloud of epicenters of the main shock and aftershocks coincides with the northern branch of the focal zone of 29.04.1991 Racha earthquake, MS = 7,0, I0 = 7?8. The focal depth of the main shock is 8 to 15 km. As the active in the focus adopted the sloping plane, plunging to the North – North-East direction. Type progress on such a plane – thrust with component of right-lateral strike-slip. Seismodislocationswere of secondary gravitational nature. The results of paleoseismological studies conducted in the Eastern part of the epicentral area of the Racha earthquake, showed that this seismic source the strong seismic shocks happened before. According to the obtained data, the age of the previous strong earthquake in the Racha – Dzhava zone (i.e., before 1991) – about 2000 years ago. Another, more ancient event occurred about 6,000 years ago. The recurrence period of strong earthquakes, similar to the disaster of 1991, thus, is an average of 2000?3000 years.

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Evolution of views on the structure of sources of strong earthquakes at the end of XX and beginning of XXI centuries

Физика земли ◽

10.31857/s0002-333720191134-148 ◽

2019 ◽

pp. 134-148

Author(s):

E. A. Rogozhin

Keyword(s):

Seismic Waves ◽

Dynamic Control ◽

3D Structure ◽

Three Dimensional ◽

Seismic Source ◽

Developed Countries ◽

Seismic Events ◽

Low Velocity ◽

Strong Earthquakes ◽

The Past

The paper addresses the evolution of scientific views on the structure of the sources of strong earthquakes at the end of the 20th and beginning of the 21th century in Russia. The scientific concepts that emerged in the main developed countries initially typically lacked a clear and consistent understanding of the structure of sources of the strongest seismic events. In the 1950s, at the Schmidt Institute of Physics of the Earth of the USSR Academy of Sciences, G.A. Gamburtsev formulated a hypothesis of a long-term (a few hundred years) stability of seismic regime of a system of seismic sutures. The recently studied earthquakes have their sources in the regions of the large faults. The earthquakes of larger magnitudes have more extended and structurally more complex sources. Some sources in the considered cases are relatively simple to reconstruct (they encompass the fault planes of the large faults, e.g., the Spitak source, M = 6.8). Other sources are more complex; they are formed in the disjunctive nodes or encompass the crustal blocks. For example, the seismic source of the Altai earthquake (M = 7.3) has a volumetric structure and is developed along the boundaries of the large seismogenic blocks. The Wenchuan earthquake (M = 7.9) has a most complicated source which looks as a three-dimensional (3D) structure composed of a few crustal blocks framed by two extended northeast striking faults and separated by the northwesterly trending transverse fault. The structurally different sources differently manifest themselves in the pattern of seismic dislocations on the surface and in the distribution of aftershock hypocenters at depth. The anomalously low velocity “pockets” identified by local seismic tomography in the source areas of the Spitak and Altai earthquakes which accompany the main and secondary faults at depth are likely to be the zones of dynamic control of these faults. The breaked near-fault zones abundant with cracks and fractures are the severely looze inclusions in the crustal rocks hampering the propagation of seismic waves. Therefore, the P-waves in these pockets propagate at lower velocities than in the undamaged geological medium. The paleoseismological studies of seismic faults in trenches have shown that the strong earthquakes have occurred in the same sources in the past and the recurrence period of the strongest seismic events ranges from a few hundred to a few thousand years. Thus, the combined studies of the source zones of the strongest earthquakes conducted in the past decades in the different regions of Eurasia have shown that Gamburtsev’s hypothesis has remained relevant.

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