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The site amplification is estimated at five seismic stations of the Latur region using the horizontal to vertical spectral ratios of 33 aftershocks of the main Killari earthquake of September 29, 1993 (UTC). Spectral amplifications, ranging from a factor of 2–6 are found to vary with frequency at different places. Significant amplification is found at four sites within the Latur region, at Basavakalyan, Kasgi, Killari, and Mudgad Eakoji villages. Our results show a positive correlation between the site amplification and the damage pattern in area. The pattern and the nature of the site amplification estimated in the present study corroborates also with the analytical models and the borehole data indicating alternating layers of unconsolidated sediments and basaltic rocks. 相似文献
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C.D. Lindholm H. Bungum R.K. Bratli B.S. Aadnøy N. Dahl B. Tørudbakken K. Atakan 《地学学报》1995,7(1):51-59
The regional stress field in the northern North Sea (offshore western Norway) has been studied through the acquisition and analysis of directions of maximum horizontal compression (H ) as extracted from borehole breakouts and from earthquake focal mechanism solutions.
The results indicate that the regional stress field is dominated by NW-SE compression, with good consistency between shallow borehole breakouts (2–5 km depth) and deeper earthquakes (10–25 km depth). The broad spatial consistency in stress direction indicates that the main stress field is related to factors of primarily plate tectonic origin, and the results are in good agreement with the western Europe trend found in earlier investigations.
The Tampen Spur region in the northern North Sea has been subjected to particularly complex deformation, with two dominating fault directions trending NW-SE and NE-SW. From Tampen Spur in the west to the Sogn graben in the east an anomalous stress field is indicated, with NE-SW oriented maximum horizontal compressions. This anomaly is clearly seen both in the borehole breakout data and in the earthquake data. Possible sources for this anomaly are discussed, and include postglacial uplift and/or lateral variations in the physical properties of the crust. 相似文献
The results indicate that the regional stress field is dominated by NW-SE compression, with good consistency between shallow borehole breakouts (2–5 km depth) and deeper earthquakes (10–25 km depth). The broad spatial consistency in stress direction indicates that the main stress field is related to factors of primarily plate tectonic origin, and the results are in good agreement with the western Europe trend found in earlier investigations.
The Tampen Spur region in the northern North Sea has been subjected to particularly complex deformation, with two dominating fault directions trending NW-SE and NE-SW. From Tampen Spur in the west to the Sogn graben in the east an anomalous stress field is indicated, with NE-SW oriented maximum horizontal compressions. This anomaly is clearly seen both in the borehole breakout data and in the earthquake data. Possible sources for this anomaly are discussed, and include postglacial uplift and/or lateral variations in the physical properties of the crust. 相似文献
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Bertrand Guillier Kuvvet Atakan Jean-Luc Chatelain Jens Havskov Matthias Ohrnberger Fabrizio Cara Anne-Marie Duval Stratos Zacharopoulos Paula Teves-Costa The SESAME Team 《Bulletin of Earthquake Engineering》2008,6(1):3-31
For an optimal analysis of the H/V curve, it appears necessary to check the instrument signal to noise ratio in the studied
frequency band, to ensure that the signal from the ground noise is well above the internal noise. We assess the reliability
and accuracy of various digitizers, sensors and/or digitizer-sensor couples. Although this study is of general interest for
any kind of seismological study, we emphasize the influence of equipment on H/V analysis results. To display the impact of
the instrumental part on the H/V behavior, some series of tests have been carried out following a step-by-step procedure:
first, the digitizers have been tested in the lab (sensitivity, internal noise...), then the three components sensors, still
in the lab, and finally the usual user digitizers-sensors couple in lab and outdoors. In general, the digitizer characteristics,
verified during this test, correspond well to the manufacturer specifications, however, depending on the digitizer, the quality
of the digitized waveform can be very good to very poor, with variation from a channel to another channel (gain, time difference
etc.). It appears very clearly that digitizers need a warming up time before the recording to avoid problems in the low-frequency
range. Regarding the sensors, we recommend strongly to avoid the use of “classical” accelerometers (i.e., usual force balance
technology). The majority of tested seismometers (broadband and short period, even 4.5 Hz) can be used without problems from
0.4 to 25 Hz. In all cases, the instrumentation should be checked first to verify that it works well for the defined study
aim, but also to define its limit of use (frequency, sensitivity...). 相似文献
5.
In recent years, there has been a growing awareness of the importance of local site effects in earthquake damage. A number of studies of recent destructive earthquakes have illustrated the relative contribution of enhanced ground shaking due to unconsolidated sediment layers.
Among the different methods used to estimate local site response, the spectral ratio of shaking at a sedimentary site with respect to a bedrock reference site, has been successfuly applied in different geological environments. In this study, a technique recently proposed by Nakamura (1989) is used to evaluate site response using spectral ratios of horizontal vs. vertical components of earthquake recordings from a temporary ocean bottom seismograph (OBS) network in the northern North Sea and a permanent OBS at Oseberg oil field. Comparison with results obtained from the standard spectral ratios, indicate that the method is applicable also to subsea conditions, and the estimates obtained in this study indicate similar amplification factors to those obtained previously from analytical techniques. The ambient noise data on the other hand, gave unstable results, probably due to different noise characteristics in the marine environment. The results obtained on the earthquake data, however, provide an encouraging alternative to previously used analytical techniques for estimating local site response. 相似文献
Among the different methods used to estimate local site response, the spectral ratio of shaking at a sedimentary site with respect to a bedrock reference site, has been successfuly applied in different geological environments. In this study, a technique recently proposed by Nakamura (1989) is used to evaluate site response using spectral ratios of horizontal vs. vertical components of earthquake recordings from a temporary ocean bottom seismograph (OBS) network in the northern North Sea and a permanent OBS at Oseberg oil field. Comparison with results obtained from the standard spectral ratios, indicate that the method is applicable also to subsea conditions, and the estimates obtained in this study indicate similar amplification factors to those obtained previously from analytical techniques. The ambient noise data on the other hand, gave unstable results, probably due to different noise characteristics in the marine environment. The results obtained on the earthquake data, however, provide an encouraging alternative to previously used analytical techniques for estimating local site response. 相似文献
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Aníbal Ojeda Kuvvet Atakan Eullia Masana Pere Santanach María-Jos Jimnez Mariano García-Fernndez 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):911-916
In this study, the influence of paleoseismic and geologic data in the seismic hazard estimation for the Catalan coastal ranges is analysed. We computed the probabilistic seismic hazard using area seismic sources with a Poissonian assumption for the earthquake occurrence. For the computations, a previously published attenuation relationship based on European strong motion data was applied. The resulting hazard estimates show similarities to the previous assessments in the region. These results were then used as a reference for comparison with other new models. In order to analyse the influence of the paleoseismic data three different models were tested. Since the number of faults that are investigated in detail are few, the same area sources that were used in the Poissonian assumption were kept in all three new models. In addition, the new paleoseismic data with faults expressed as line sources were used. In this case, a cyclic earthquake occurrence was assumed. The three models were based on the paleoseismic data with different assumptions on the time elapsed since last event. The time elapsed was set to 0, 10 and 85% of the recurrence interval in each model. The results are presented as maps showing the difference between the three models and the reference model with the Poissonian assumption. The results are given in horizontal peak ground acceleration contour maps for different return periods, also taking into account large return periods as high as 25,000 years. This is done to demonstrate the effect of large recurrence intervals found for some of the active faults. In general, we observe that for short return periods (<1000 years), the Poissonian assumption of earthquake occurrence is probably sufficient and provides a robust estimate of the hazard. However, for longer return periods (>5000 years) the effects of the paleoseismic data become increasingly significant. In order to estimate the true seismic hazard potential of this apparently low seismicity area, long-term behaviour of the possible active faults in the region needs to be investigated systematically. 相似文献
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On the first of January 1992, unusual earthquake activity started in Steigen, northern Norway. By 31 December, 1992, a total of 207 events had been recorded in several pulses. Among these, several events with magnitudes larger than 3.0 ( M c ) were also felt by the people. The epicentral distribution of these events seems to suggest that they all are concentrated in a small region (approximately 10 km in diameter) in the Brennvika Bay (67.8°N, 14.9°E), between Leinesfjorden in the north and Nordfolda in the south. The distribution of events in time is characteristic of a swarm in which no dear evidence of a mainshock–aftershock sequence was observed. Macroseismic intensity surveys as well as synthetic modelling indicate shallow focal depths in the range 5–8 km. Based on a composite focal mechanism, indicating an oblique-slip fault striking NE with a normal component dipping NW, combined with an observed NE trend in the epicentres and the focal depths, these events correlate with a previously proposed fault zone along Nordfolda. The NE trend has been dominant in the area throughout geological time, starting from the Caledonian Orogeny to the post-Caledonian basin developments, as well as the post-glacial and neotectonic structural features. At present, the deep-seated structural anomaly underneath the Lofoten Ridge seems to be the major factor controlling the structural trends in the area. The activity along the Nordfolda fault zone could be related to this large-scale structure, although the causes of the stresses that would create the seismic activity are not very clear, as there are several possible stress-generating mechanisms involved, such as post-glacial uplift of the land masses, the 'ridge-push' effect from Mohn's Ridge, and vertical stresses generated by the sediment loading in the adjacent basins. 相似文献
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Mathilde Bøttger Sørensen Peter H. Voss Jens Havskov Søren Gregersen Kuvvet Atakan 《Journal of Seismology》2011,15(4):599-611
The seismically active Skagerrak region in the border area between Denmark and Norway has traditionally been associated with
uncertain earthquake locations due to the limited station coverage in the region. A new seismic station in southern Norway
and a recent update of the earthquake database of the Danish National Network have led to a much more complete and homogeneous
data coverage of the Skagerrak area, giving the possibility of improved earthquake locations in the region. In this study,
we relocate earthquakes in the Skagerrak area to obtain a more exact picture of the seismicity and investigate well-recorded
events to determine the depth distribution. Hypocenter depths are found to be generally in the range 11–25 km. Furthermore,
new composite focal mechanisms are determined for clusters of events with similar waveforms. Results indicate that the Skagerrak
seismicity is associated with shallow, crustal faults oriented in the NS direction south of the Sorgenfrei–Tornquist Zone
(STZ) as well as with the STZ itself. Mainly reverse faulting mechanisms along NE–SW oriented faults indicate maximum horizontal
compression in the NW–SE direction. This is in agreement with World Stress Map generalizations, most likely associated with
ridge push forces from the mid-Atlantic ridge, though modified probably by local crustal weaknesses. 相似文献
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