Earthquake Of Magnitude Ms Research Articles

Back analysis of ground vibrations which cause cracks in buildings in residential areas Karakuyu (Dinar, Afyonkarahisar, Turkey)

The Karakuyu village (Dinar) is located in the south-western Turkey. Karakuyu settlement area suffered from ground vibration. There are two reasons for ground vibration in that area. One of them is earthquake and other is rock blasting. Geological structure and tectonics have great influence on vibrations in the area. An earthquake of magnitude Ms = 6.1 occurred on 1 October 1995, causing causalities and damage to buildings in Dinar and its vicinity. The earthquake forces during the main shock were amplified by poor dynamic characteristics of alluvial soils, thus resulting in damage to buildings. Limestone quarries are other source of ground vibration because of blasting. In this study, the source of vibration causing cracks in buildings in the Karakuyu residential area was investigated. Blasting at limestone quarries and past earthquake activities are analysed of ground vibrations which cause cracks in buildings. In the scope of this study, the source of the vibrations which cause the observed cracks in buildings were investigated using back analysis. As a result of the study, earthquake-induced vibrations on structural behaviour of buildings were found critical.

Some preliminary results of a worldwide seismicity estimation: a case study of seismic hazard evaluation in South America

Global data have been widely used for seismicity and seismic hazard assessment by seismologists. In the present study we evaluate worldwide seismicity in terms of maps of maximum observed magnitude (Mmax), seismic moment (M 0 ) and seismic moment rate (M 0S). The data set used consists of a complete and homogeneous global catalogue of shallow (h £ 60 km) earthquakes of magnitude MS ³ 5.5 for the time period 1894-1992. In order to construct maps of seismicity and seismic hazard the parameters a and b derived from the magnitude-frequency relationship were estimated by both: a) the least squares, and b) the maximum likelihood, methods. The values of a and b were determined considering circles centered at each grid point 1° (of a mesh 1° ´1°) and of varying radius, which starts from 30 km and moves with a step of 10 km. Only a and b values which fulfill some predefined conditions were considered in the further procedure for evaluating the seismic hazard maps. The obtained worldwide M max distribution in general delineates the contours of the plate boundaries. The highest values of M max observed are along the circum-Pacific belt and in the Himalayan area. The subduction plate boundaries are characterized by the largest amount of M 0 , while areas of continental collision are next. The highest values of seismic moment rate (per 1 year and per equal area of 10 000 km 2) are found in the Southern Himalayas. The western coasts of U.S.A., Northwestern Canada and Alaska, the Indian Ocean and the eastern rift of Africa are characterized by high values of M 0 , while most of the Pacific subduction zones have lower values of seismic moment rate. Finally we analyzed the seismic hazard in South America comparing the predicted by the NUVEL1 model convergence slip rate between Nazca and South America plates with the average slip rate due to earthquakes. This consideration allows for distinguishing between zones of high and low coupling along the studied convergence plate boundary.

Recent deformation in the Turan and South Kazakh platforms, western central Asia, and its relation to Arabia‐Asia and India‐Asia collisions

In this study, we investigate the recent and active tectonics of the Turan and South Kazakh platforms in western central Asia. This area, which has been considered stable during the Tertiary, was struck in its eastern part (Gazli and Kyzyl‐Kum) by three earthquakes of magnitude Ms ∼7.0 between 1976 and 1984. From structural observations we show that in the Kyzyl‐Kum, Cenozoic deformation on structures oriented NW–SE is dominated by dextral strike‐slip motion on a flower structure involving reactivated Late Paleozoic faults. This deformation is compatible with the stress pattern induced by the Pamir/Tien Shan collision zone. At the scale of the Turan‐South Kazakh platform, comparison of repeated leveling measurements gives mean uplift rates of 5 mm yr−1 for most of the area south of the 44° latitude including the Kyzyl‐Kum. These observations indicate that the Turan‐South Kazakh platform has been actively deforming since recent times (Pleistocene) in response to the collision of both India and Arabia with Asia. Earthquake data also reveal that propagation of deformation from the Kopet Dagh and the Pamir/Tien Shan collision zones into the Turan‐South Kazakh platform is accommodated aseismically except in the Kyzyl‐Kum. This might reflect differences in the deformation style and nature of the upper crust in the Kyzyl‐Kum and north of the Kopet Dagh respectively. We propose that the Gazli earthquakes highlight the northwestward continuation, within the Turan‐South Kazakh platform and along reactivated older structures, of the deformation related to the Pamir indentation and to a lesser degree to the Arabia‐Asia convergence.

Report on the Earthquake of September 14, 1995, in Guerrero, Mexico

On September 14, 1995, at 8:04 AM, local time (14:04, GMT), an earthquake of magnitude Ms = 7.2 (Mw = 7.3) took place in the Pacific coast of the State of Guerrero, Mexico, close to the town of Copala, with epicenter located at 16.7°N and 98.5°W. The shallow focal depth (17.5 km), the focal mechanism (thrust) and the low dip angle indicate that it is a typical earthquake of the Mexican subduction zone, in the interface between the North American and Cocos plates. Table 1 gives some basic seismological parameters, as well as some values of recorded peak ground acceleration (PGA) that might be of interest. The earthquake produced high intensities in the epicentral area, where it caused considerable damage in some villages in South Guerrero and Southwest Oaxaca. The region is sparsely populated, so only six people died, although 2,000 people remained homeless and more than 5,000 houses were...

Propagation and amplification of tsunamis at coastal boundaries

WHEN tsunamis hit a coastal area, they often cause substantial damage and loss of life at locations otherwise well protected from normal (even severe) wind-generated waves. An example of such a catastrophe took place on 12 December 1992, when an earthquake of magnitude Ms = 7.5 occurred in the eastern region of Flores Island, Indonesia1,2. One of the areas hardest hit by the resulting tsunamis was Babi, a small coastal island; two villages on the island were completely destroyed, even though both were located in sheltered areas where wave conditions are normally calm. Here we describe the results of numerical and laboratory experiments that show how, unlike wind-generated waves, tsunamis are capable of penetrating into sheltered coastal areas without significantly losing their energy. For the case of Babi Island, the original tsunami wave was split into two, with one wave propagating around each side of the island. The two waves met in the sheltered region, and the subsequent amplification of wave amplitude resulted in the destructive flow onto the beach.

The Flores Island tsunamis

On December 12, 1992, at 5:30 A.M. GMT, an earthquake of magnitude Ms 7.5 struck the eastern region of Flores Island, Indonesia (Figure 1), a volcanic island located just at the transition between the Sunda and Banda Island arc systems. The local newspaper reported that 25‐m high tsunamis struck the town of Maumere, causing substantial casualties and property damage. On December 16, television reports broadcast in Japan via satellite reported that 1000 people had been killed in Maumere and twothirds of the population of Babi Island had been swept away by the tsunamis.The current toll of the Flores earthquake is 2080 deaths and 2144 injuries, approximately 50% of which are attributed to the tsunamis. A tsunami survey plan was initiated within 3 days of the earthquake, and a cooperative international survey team was formed with four scientists from Indonesia, nine from Japan, three from the United States, one from the United Kingdom, and one from Korea.

The Constantine (northeast Algeria) earthquake of October 27, 1985: surface ruptures and aftershock study

An earthquake of magnitude Ms = 6.0 (CSEM, Strasbourg) occurred at Constantine (Algeria) on 27 October 1985. This seismic event is the strongest felt in the Tellian Atlas since the El Asnam seismic crisis of October 10, 1980. A team from the Centre de Recherche d'Astronomie, d'Astrophysique et de Géophysique (CRAAG, Algeria), utilising 8 portable stations, registered the activity a few days after the main shock. The aftershocks follow a N045° direction, and show the existence of three ruptured segments. Cross sections display a remarkable vertical fault plane and suggest asperities in the rupture process. Surface breaks were found affecting Quaternary deposits. The principal segment is about 3.8 km long showing “enéchelon” cracks with left-lateral displacement while the main direction of the rupture is N055°. Although the vertical motion is small, the northwestern block shows a normal component of the main surface faulting, while the left-lateral displacement is about 10 cm. The strike-slip focal mechanism solution determined from the global seismic network and field observations are in good agreement.

Earthquake faulting and bedding thrust associated with the Tabas-e-Golshan (Iran) earthquake of September 16, 1978

abstractThe Tabas-e-Golshan earthquake of magnitude Ms = 7.7 occurred in a region of east central Iran known to have been quiescent for at least 11 centuries. The shock was associated with 85 km of discontinuous thrust faulting at the surface along an existing but unrecognized late Quaternary fault (the Tabas Fault). Nearly all the surface breaks followed the obvious scarps created by the previous faulting. An extensive zone of “bedding thrusts” (bedding-plane slip) was also developed in the Neogene clay deposits of the overthrust block, east of the main fault zone. Minimum vertical uplift (throw) and slip measured at about 150 and 300 cm, respectively. The deformation caused by this earthquake indicates crustal thickening of the region, i.e. uplifting along the earthquake fault. The Tabas Fault is one of the principal structures by which the western flank of the Shotori mountains is raised about 2 km above the alluvial deposits of the Tabas compressional graben. It is a multi-role deep-seated Precambrian fault and one of the major features during Paleozoic and Mesozoic, in the western part of the fault-controlled subsiding sedimentary basin of Shotori.The earthquake killed more than 20,000 people and severely damaged or destroyed about 90 villages together with the town of Tabas. This catastrophic event emphasizes once more the importance of mapping recent faults and the careful field study of structures associated with low-magnitude buried earthquakes. In the case of Tabas, the lack of historical seismic damage over the past 11 centuries meant that there was no adequate assessment of the seismicity and seismic hazard on this basis. A comparison of the Plio-Pleistocene and Late Quaternary crustal deformation with that associated with this earthquake indicates the intra-plate deformation to be essentially unchanging since that time, and the regional stress field to be not greatly changed since the late Alpine phase.The present state of knowledge about regional tectonics and seismicity suggests the country to be a broad zone of compressional deformation, the present deformation being taken up mostly by the existing late Quaternary mountain-bordering reverse faults inherited from the old geological times. The seismicity is widespread along several faults and the continental crust is thickening and shortening in the NE-SW direction.