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Search Results: 1 - 10 of 2038 matches for " earthquake tectonics "
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Basement Configuration from Magnetotelluric Studies in Bhuj Earthquake Epicentral Zone, Gujarat, India  [PDF]
S. Kareemunnisa Begum, T. Harinarayana
Open Journal of Earthquake Research (OJER) , 2016, DOI: 10.4236/ojer.2016.53015
Abstract: A wide band (1000 - 0.001 Hz) magnetotelluric study has been taken up in the Bhuj earthquake epicentral zone and 21 sites have been occupied along three profiles during March-April 2001 to understand the deep structure of the region. In addition the region surrounding Bhuj has been probed earlier with number of MT profiles and the subsurface structure is well constrained from hydrocarbon exploration point of view besides seismotectonic studies. In the present study, the results obtained along 130 km long profile from Mundra to Rapar oriented in NE-SW direction passing through the epicenter are presented considering these two databases. The subsurface structure has shown interesting correlation with the surface deformations, a new basement configuration and associated seismotectonics of the region. Our main result is relating the basement configuration and surface ruptures.
Paleoearthquakes and slip rates of the North Tabriz Fault, NW Iran: preliminary results
K. Hessami,D. Pantosti,H. Tabassi,E. Shabanian
Annals of Geophysics , 2003, DOI: 10.4401/ag-3461
Abstract: The North Tabriz Fault is a major seismogenic fault in NW Iran. The last damaging earthquakes on this fault occurred in 1721, rupturing the southeastern fault segment, and in 1780, rupturing the northwestern one. The understanding of the seismic behavior of this fault is critical for assessing the hazard in Tabriz, one of the major cities of Iran; the city suffered major damage in both the 1721 and 1780 events. Our study area is located on the northwestern fault segment, west of the city of Tabriz. We performed geomorphic and trenching investigations, which allowed us to recognize evidence for repeated faulting events since the Late Pleistocene. From the trenches, we found evidence for at least four events during the past 3.6 ka, the most recent one being the 1780 earthquake. On the basis of different approaches, horizontal slip per event and slip rates are found in the ranges of 4 ± 0.5 m and 3.1-6.4 mm/yr, respectively. We also attempted an estimate of the average recurrence intervals which appears to be in the range 350-1430 years, with a mean recurrence interval of 821 ± 176 years. On the basis of these results, the northwestern segment of the North Tabriz Fault does not appear to present a major seismic potential for the near future, however, not enough is known about the southeastern segment of the fault to make a comparable conclusion.
THE EARTHQUAKE AND TSUNAMI OF JULY 21, 365 AD IN THE EASTERN MEDITERRANEAN SEA - Review of Impact on the Ancient World - Assessment of Recurrence and Future Impact
George Pararas-Carayannis
Science of Tsunami Hazards , 2011,
Abstract: There is ample evidence indicating that on July 21, 365 AD a great earthquake near the west coast of the Island of Crete generated a mega-tsunami, which was responsible for extensive destruction throughout the Eastern Mediterranean, but particularly on Peloponnesus, the Greek Islands, Sicily, Libya, Cyprus, Palestine and Egypt. It is believed that the combined catastrophic impacts of the earthquake and tsunami were significant catalysts in furthering the declination of the Roman Empire and contributing to its subsequent final division between the East Roman and the West (Byzantine) empires in 395 A.D. In view of subsequent earthquakes and tsunamis in the region and the high probability that a similar great disaster will occur again, the present study reviews and summarizes the seismo-tectonic and kinematic characteristics of the Aegean and Anatolian micro-plates, their interaction with the African and Eurasian tectonic plates and examines and evaluates the historical records pertaining to this 4th Century AD disaster as to the destructive impact it had on the ancient world. Additionally, the study reconciles the impact described in historical and recent records with results obtained by numerical modeling studies, provides a rough estimate of the recurrence frequency of great tsunamigenic earthquakes in the Eastern Mediterranean region and assesses what the future impact may be in view of great increases in population densities along coastal areas.
Casos históricos colombianos del registro de anomalías del radón-222 antes de eventos sísmicos de naturaleza tectónica
Serna Valencia Doris Yaneth,Moran Rodríguez Estela Catalina,Garzón Valencia Gustavo,Hernández Silva Mónica Lucia
Earth Sciences Research Journal , 2003,
Abstract: Since 1995 it had been making continuous measurements of the radioactive isotope Radon-222 emissions in soils at Galeras and Nevado del Ruiz volcanoes; and on active geological faults in Nari o, Cauca and Caldas districts. The E-PERM ionizing chamber system has been used in the Radon-222 monitoring, trapping this gas in the B horizont of soils. In zones of active faulting it has been stablished Radon soil emissions between 1000 and 2500 pCi/L. In some crossings of active faults it has been measured levels of25000 pCilL. In the present work appears a compilation of examples of the registered anomalous emissions in several stations before earthquakes of tectonic character. Examples of registered Radon anomalies before: I) events of magnitudes between 2 and 4; 2) the Quindío earthquake of january 1999; and 3) the occurrence of seismic swarms registered by the seismological networks of the Volcanological and Seismological Observatories at Pasto and Manizales, are described. Desde el a o de 1995 se han estado realizando mediciones continuas de las emisiones del isótopo radiactivo Radón-222 en los suelos de los volcanes Galeras y nevado del Ruiz, y sobre fallas activas en los departamentos de Nari o, Cauca y Caldas. En el monitoreo del gas Radón-222 se ha utilizado el sistema de medición de cámaras ionizantes E-PERM, atrapando los gases en el horizonte B de los suelos. Se ha encontrado que en zonas de fallamiento activo las emisiones de este gas están entre los 1000 Y2500 pCi/L. En algunos cruces de fallas activas se han medido niveles hasta de 25000 pCi/L. En el presente trabajo se presenta una compilación de ejemplos de las emisiones anómalas registradas en varias estaciones antes de sismos de carácter tectónico. Se muestran anomalías del Radón registradas antes de: I) eventos de magnitudes entre 2 y 4; 2) el terremoto del Quindío de enero de 1999, y 3) la ocurrencia de enjambres sísmicos registrados por las redes sismológicas de los observatorios vulcanológicos y sismológicos de Pasto y Manizales.
The earthquake of 12 April 1998 in the Krn Mountains (Upper So a valley, Slovenia) and its seismotectonic characteristics
Polona Zupan?i?,Ina Ceci?,Andrej Gosar,Ladislav Placer
Geologija , 2001,
Abstract:
A probabilistic seismic hazard map of India and adjoining regions
S. C. Bhatia,M. R. Kumar,H. K. Gupta
Annals of Geophysics , 1999, DOI: 10.4401/ag-3777
Abstract: This paper presents the results of an exercise carried out under GSHAP, over India and adjoining regions bound by 0°N-40°N and 65°E-100°E. A working catalogue of main shocks was prepared by merging the local catalogues with the NOAA catalogue, and removing duplicates, aftershocks and earthquakes without any magnitude. Eighty six potential seismic source zones were delineated based on the major tectonic features and seismicity trends. Using the probabilistic hazard assessment approach of McGuire, adopted by GSHAP, the Peak Ground Accelerations (PGA) were computed for 10% probability of exceedance in 50 years, at locations defined by a grid of 0.5° x 0.5°. Since no reliable estimates of attenuation values are available for the Indian region, the attenuation relation of Joyner and Boore (1981) was used. The PGA values over the grid points were contoured to obtain a seismic hazard map. The hazard map depicts that a majority of the Northern Indian plate boundary region and the Tibetan plateau region have hazard level of the order of 0.25 g with prominent highs of the order of 0.35-0.4 g in the seismically more active zones like the Burmese arc, Northeastern India and Hindukush region. In the Indian shield, the regional seismic hazard, covering a major area, is of the order of 0.05-0.1 g whereas some areas like Koyna depict hazard to the level of 0.2 g. The present map can be converted into a conventional seismic zoning map having four zones with zone factors of 0.1 g, 0.2 g, 0.3 g and 0.4 g respectively.
Active tectonics and earthquake destructions in caves of northern and central Switzerland
Becker Arnfried,H?uselmann Philipp,Eikenberg Jost,Gilli Eric
International Journal of Speleology , 2012,
Abstract: The present publication focuses on the study of caves in northern and central Switzerland in order to detect and date historical earthquakes and active tectonic displacements by investigations of broken and resealed or displaced speleothems datable by U/Th and 14C. While it can be shown that these methods are potentially suitable, the ages obtained are often beyond the range of historically recorded earthquakes, and it cannot be proved that the observed and dated events are related to a seismic event. Particularly this is true for the caves in central Switzerland, where most ages in the Melchsee-Frutt region were beyond the limits of the U/Th method, or of late Pleistocene age in the Siebenhengste-Hohgant region. A direct comparison with known historical (or prehistoric) earthquakes was not possible. In contrast to central Switzerland, the results in the Basle region of northern Switzerland indicates cave and speleothem damages in one cave within the epicentral area of the 1356 Basle earthquake. 14C datings allowed to directly relate the speleothem damages to this M 6.9 earthquake. Further dating results from caves in northern Switzerland on speleothems and organic material in cave deposits supplied ages which indicate older events not related to the historical Basle earthquake. The detection of active fault displacements and prehistoric strong earthquakes can only be achieved by a very careful deciphering of the palaeo-environmental records and many more age determinations which allow to separate active tectonic displacements and seismic events from other events not related to tectonics, i.e. glaciations, creep of sediments, catastrophic floods etc.
Characteristics of the crustal structure and hypocentral tectonics in the epicentral area of Nan’ao earthquake (M7.5), the northeastern South China Sea
Huilong Xu,Xuelin Qiu,Minghui Zhao,Jinlong Sun,Junjiang Zhu
Chinese Science Bulletin , 2006, DOI: 10.1007/s11434-006-9095-x
Abstract: 1918 Nan’ao earthquake (M7.5) occurred in the northeast coastal areas of Guangdong Province. With the seismogeological survey of the epicentral area and history materials analyses, the earthquake epicenter was estimated to locate in the intersection part of the Binhai fault zone (Littoral) and Huanggangshui fault, which strikes NEE and NW, respectively. The activities of the NEE-striking thrust fault and NW-striking extensional fault that were attributed to 1918 Nan’ao earthquake occurred in the Dongshan Island of the epicentral area; they reflected the focal stress field with compression in NW-SE direction and extension in NE-SW direction. The isoseismal contour of seismic intensity X shows a shape of ‘X’ composed of two mutually overlapping ellipses with two axes striking NEE and NW, respectively, and such shape implies that the occurrence of this earthquake is controlled by a pair of conjugate seismotectonic faults constituted by the NEE-striking Binhai fault zone and the NW-striking Huanggangshui fault. The Binhai fault zone is a dominant seismogenic structure, and the NW-striking Huanggangshui fault is the subdominant one. The onshore-offshore deep seismic profile that crossed the epicentral area and was perpendicular to the strike of the Binhai fault zone was obtained. According to the analyses of the seismic data, the Binhai fault zone is defined as a low velocity zone with SE dip-slip in the crustal structure section. The Binhai fault zone is a boundary fault between the South China subplate and South China Sea subplate. The crust structure on the northwest side of Binhai fault zone is a normal continental crust with a thickness of 30 km, and the one on the southeast side of the fault zone is a thinning continental crust with a thickness of 25–28 km. The Binhai fault zone is an important seismogenic fault and also is an earthquake-controlling fault. The intersection part between the Binhai fault zone and the low velocity zone of upper crust is advantageous to stress concentration and strain energy accumulation, and presents the deep dynamic conditions for the earthquake’s pregnancy and occurrence.
The tectonic condition and the feature of surface rupture zone of the Mani earthquake (Ms 7.9) in 1997
1997年玛尼79级地震的构造环境和地表破裂带特征

SHAN Xin-Jian,LI Jian-Hua,ZHANG Gui-FangState Key Laboratory of Earthquake Dynamics,
单新建
,李建华,张桂芳

地球物理学报 , 2006,
Abstract: 1997年11月8日西藏玛尼7.9级地震发生在羌塘盆地北缘.本文利用LANDSAT影像,研究地震的地质构造背景,研究表明玛尼7.9级地震发生在NEE向玛尔盖茶卡—若拉错断裂带上,这是一条全新世明显活动的地壳深断裂.利用CBERS_1影像,研究地震地表破裂带的几何特征,100000分之一CBERS_1影像上由地震裂缝、地震陡坎和断塞塘组合显示的线性影像清楚地反映出地震地表主破裂带的形迹,可有效地进行破裂带的分段和长度量测.结果表明玛尼7.9级地震形成的地震地表主破裂带西起羌塘盆地北缘,绥加山南麓的白雪湖湖积平原上,向东延伸到双端湖西岸,长110km,走向N70-80°E.可分为白雪湖—玛尔盖茶卡、玛尔盖茶卡—朝阳湖、朝阳湖—双端湖3段.多时相MSS、TM影像分析表明,1997年玛尼7.9级地震是先存地震地表破裂带再次破裂的结果.
Locating the Focus of a Starting Earthquake  [PDF]
Alexander Ivanchin
International Journal of Geosciences (IJG) , 2014, DOI: 10.4236/ijg.2014.510096
Abstract: This article describes a method of locating the focus of a starting earthquake based on the use of the elastic interaction energy. The method allows determining the focus location and its energy class as well as evaluating the stresses caused by it and observing its evolution.
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