首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
  相似文献   

2.
The occurrence time of earthquakes can be anticipated or delayed by external phenomena that induce strain energy changes on the faults. ??Anticipated?? earthquakes are generally called ??triggered??; however, it can be controversial to label a specific earthquake as such, mostly because of the stochastic nature of earthquake occurrence and of the large uncertainties usually associated to stress modelling. Here we introduce a combined statistical and physical approach to quantify the probability that a given earthquake was triggered by a given stress-inducing phenomenon. As an example, we consider an earthquake that was likely triggered by a natural event: the M?=?6.2 13 Jan 1976 Kópasker earthquake on the Grímsey lineament (Tj?rnes Fracture Zone, Iceland), which occurred about 3?weeks after a large dike injection in the nearby Krafla fissure swarm. By using Coulomb stress calculations and the rate-and-state earthquake nucleation theory, we calculate the likelihood of the earthquake in a scenario that contains only the tectonic background and excludes the dike and in a scenario that includes the dike but excludes the background. Applying the Bayes?? theorem, we obtain that the probability that the earthquake was indeed triggered by the dike, rather than purely due to the accumulation of tectonic strain, is about 60 to 90?%. This methodology allows us to assign quantitative probabilities to different scenarios and can help in classifying earthquakes as triggered or not triggered by natural or human-induced changes of stress in the crust.  相似文献   

3.
During the microzonation studies of the April 6th, 2009 L??Aquila earthquake, we observed local seismic amplifications in the Roio area??a plane separated from L??Aquila city center by mount Luco. Six portable, digital instruments were deployed across the plain from 15 April to mid-May 2009. This array recorded 152 aftershocks. We analyzed the ground motion from these events to determine relative site amplification within the plain and on surrounding ridges. Horizontal over vertical spectral ratio on noise data (HVSRN), aftershock recordings (HVEQ) and standard spectral ratio (SSR) showed amplifications at 1.3 and 4.0?Hz on quaternary deposits. Seismic amplifications in the frequency range of 4 and 6?Hz were also observed on a carbonate ridge of Colle di Roio, on the northwestern border of the plateau. A small amplification was noticed near the top of mount Luco, another rocky site. Large discrepancies in the amplification levels between methods have been observed for these sites, but the HVSRN, HVEQ and SSR gave similar results at the stations located in the Roio plain. On the rocky sites, the SSR was more reliable than the HVSRN at estimating the transfer function of the site, even if the resonance frequency seemed to be well detected by the latter method.  相似文献   

4.
More damaging tsunamis have impacted Crescent City, California in historic times than any other location on the West Coast of the USA. Crescent City??s harbor has undergone significant modification since the early 20th century, including construction of several breakwaters, dredging, and a 200?×?300?m2 small boat basin. In 2006, a M w 8.3 earthquake in the Kuril Islands generated a moderate Pacific-wide tsunami. Crescent City recorded the highest amplitudes of any tide gauge in the Pacific and was the only location to experience structural damage. Strong currents damaged docks and boats within the small boat basin, causing more than US?$20 million in damage and replacement costs. We examine how modifications to Crescent City??s harbor may have affected its vulnerability to moderate tsunamis such as the 2006 event. A bathymetric grid of the basin was constructed based on US Army Corps of Engineers soundings in 1964 and 1965 before the construction of the small boat basin. The method of splitting tsunamis was used to estimate tsunami water heights and current velocities at several locations in the harbor using both the 1964?C1965 grid and the 2006 bathymetric grid for the 2006 Kuril event and a similar-sized source along the Sanriku coast of Japan. Model velocity outputs are compared for the two different bathymetries at the tide gauge location and at six additional computational sites in the harbor. The largest difference between the two grids is at the small boat basin entrance, where the 2006 bathymetry produces currents over three times the strength of the currents produced by the 1965 bathymetry. Peak currents from a Sanriku event are comparable to those produced by the 2006 event, and within the boat basin may have been higher. The modifications of the harbor, and in particular the addition of the small boat basin, appear to have contributed to the high current velocities and resulting damage in 2006 and help to explain why the 1933 M w 8.4?C8.7 Sanriku tsunami caused no damage at Crescent City.  相似文献   

5.
Disaggregation of the seismic hazard has become a popular technique to convey information on the main sources contributing to the hazard at a particular site. Recently published work adopts geographic disaggregation analysis of seismic hazard as a tool to identify dominant rupture scenarios for municipalities in Mainland Portugal. The authors conclude that the seismic hazard in South and Central Portugal is dominated by the seismicity that takes place offshore, around 70km WSW of Cape S. Vicente, both for the return periods of 475 years and 975 years. Whilst recognizing the merits of the approach taken and the utility of the tools developed, we take issue with this last conclusion. We consider that the proposed disaggregation returns a picture of the biases in the hazard analysis, more than any real feature of the distribution of relevant seismogenic sources.  相似文献   

6.
  相似文献   

7.
On 22 January 2003, the M w?=?7.6 Tecomán earthquake struck offshore of the state of Colima, Mexico, near the diffuse triple junction between the Cocos, Rivera, and North American plates. Three-hundred and fifty aftershocks of the Tecomán earthquake with magnitudes between 2.6 and 5.8, each recorded by at least 7 stations, are relocated using the double difference method. Initial locations are determined using P and S readings from the Red Sismológica Telemétrica del Estado de Colima (RESCO) and a 1-D velocity model. Because only eight RESCO stations were operating immediately following the Tecomán earthquake, uncertainties in the initial locations and depths are fairly large, with average uncertainties of 8.0?km in depth and 1.4?km in the north?Csouth and east?Cwest directions. Events occurring between 24 January and 31 January were located using not only RESCO phase readings but also additional P and S readings from 11 temporary stations. Average uncertainties decrease to 0.8?km in depth, 0.3?km in the east?Cwest direction, and 0.7?km in the north?Csouth direction for events occurring while the temporary stations were deployed. While some preliminary studies of the early aftershocks suggested that they were dominated by shallow events above the plate interface, our results place the majority of aftershocks along the plate interface, for a slab dipping between approximately 20° and 30°. This is consistent with the slab positions inferred from geodetic studies. We do see some upper plate aftershocks that may correspond to forearc fault zones, and faults inland in the upper plate, particularly among events occurring more than 3?months after the mainshock.  相似文献   

8.
  相似文献   

9.
On 6th April 2009 an earthquake of magnitude M w =  6.3 occurred in the Abruzzo region; the epicentre was very close to the city of L’Aquila (about 6 km away). The event produced casualties and damage to buildings, lifelines and other infrastructures. An analysis of the main damage that reinforced concrete (RC) structures showed after the event is presented in this study. In order to isolate the main causes of structural and non-structural damage, the seismological characteristics of the event are examined, followed by an analysis of the existing RC building stock in the area. The latter issue came under scrutiny after the release of official data about structural types and times of construction, combined with a detailed review of the most important seismic codes in force in the last 100 years in Italy. Comparison of the current design provisions of the Italian and European codes with previous standards allows the main weaknesses of the existing building stock to be determined. Damage to structural and non-structural elements is finally analyzed thanks to photographic material collected in the first week after the event; the main causes of damage are then inferred.  相似文献   

10.
In Italy infills and partitions (non-structural elements) are typically made up of hollow brick masonry, disposed in one or two parallel vertical walls. Many studies have analysed their role on the seismic behaviour of moment resisting framed RC buildings and many seismic codes, all over the world, have provided specific additional measures for them. During the Abruzzo seismic sequence, non-structural damage in RC buildings, both private and public, was extensive, varying from small cracks to collapse, along with minor or no damage to structural elements. This damage involved a number of buildings, both old and recently completed, determining heavy socio-economic consequences, including human casualties, loss of building functionality (particularly important in case of strategic constructions), and unusable buildings. In this paper a review of the most frequent damage patterns is performed, aimed at identifying the main causes of damage and linking them to commonly adopted construction rules. For this purpose, local and global structural configurations frequently exhibiting non-structural damage are described, aside from out-of-plane and in-plane failures. Furthermore, a review of code provisions on non structural elements has been performed in the paper making reference to the most prominent current seismic codes and, finally, some design and construction rules are suggested.  相似文献   

11.
Aftershock locations, source parameters and slip distribution in the coupling zone between the overriding North American and subducted Rivera and Cocos plates were calculated for the 22 January 2003 Tecomán earthquake. Aftershock locations lie north of the El Gordo Graben with a northwest-southeast trend along the coast and superimposed on the rupture areas of the 1932 (M w?=?8.2) and 1995 (M w?=?8.0) earthquakes. The Tecomán earthquake ruptured the northwest sector of the Colima gap, however, half of the gap remains unbroken. The aftershock area has a rectangular shape of 42?±?2 by 56?±?2?km with a shallow dip of roughly 12° of the Wadati-Benioff zone. Fault geometry calculated with the Náb??lek (1984) inversion procedure is: (strike, dip, rake)?=?(277°, 27°, 78°). From the teleseimic body wave spectra and assuming a circular fault model, we estimated source duration of 20?±?2?s, a stress drop of 5.4?±?2.5?MPa and a seismic moment of 2.7?±?.7?×?1020?Nm. The spatial slip distribution on the fault plane was estimated using new additional near field strong motion data (54?km from the epicenter). We confirm their main conclusions, however we found four zones of seismic moment release clearly separated. One of them, not well defined before, is located toward the coast down dip. This observation is the result of adding new data in the inversion. We calculated a maximum slip of 3.2?m, a source duration of 30?s and a seismic moment of 1.88?×?1020?Nm.  相似文献   

12.
  相似文献   

13.
On April 6, 2009 a ML = 5.8 earthquake hit the city of L’Aquila on the Apennine chain in central Italy. Notwithstanding the moderate-size event the L’Aquila city and several small villages along the Aterno river valley suffered severe damage, because of the unusual strong motions, mainly due to proximity to the fault (estimated hypocentral depth of about 10 km). In this paper the main features of the recorded motion are discussed. Four accelerometric stations were located within the surface projection of the fault and recorded peak values ranging from 0.4 to 0.6 g. The recorded motions were characterised by short durations and high peak accelerations both in the horizontal and vertical directions. The strong portions of vertical and horizontal motions occurred almost simultaneously due to the short travel paths of P and S waves from the fault to the ground surface near the fault area. Hence site response analyses were performed for the sites where recording stations were located. The geotechnical subsoil model was derived by boreholes, in situ dynamic tests (D-H and SDMT) and by laboratory tests (RCT). One-dimensional numerical analyses were carried out employing the well known computer code EERA. The numerical model was calibrated, in the linear equivalent range, by comparing numerical results with the horizontal acceleration recorded components.  相似文献   

14.
In this study near field strong ground motion generation of Mw 6.9 scenario events on Gemlik Bay was presented at broadband frequency (0.5–10 Hz) ground motion at 9 stations. In the first stage of the study, focal mechanism of a small earthquake, which was used as the Empirical Green’s Function (EGF) throughout the scenario simulation, was decided by simulating it with a smaller magnitude event. The best waveform fitting was judged with the smallest misfit value. In the second stage, near field ground motion simulation of scenario events was performed. Calculations were achieved by considering three different rupture processes which have the same magnitude but different asperity locations. Fault and asperity parameters for each scenario were determined from empirical scaling laws. It has been found that the peak ground acceleration and peak ground velocities reach maximum values of 1,440 cm/s2 and 125 cm/s, respectively for the worst case scenario. Rupture directivity effect is observed with clear peaks at a forward station. The design spectra for Turkish seismic design code (TSDC 2007) were either nearly or actually exceeded by the scenario earthquakes at periods lower than 0.6  s at all near field stations. Majority of structures in the area were built to lower design spectra before the 1998 code was implemented. The strength of many structures would have been insufficient to resist the forces that may be generated by an earthquake that is similar to Scenario I and Scenario II in this study.  相似文献   

15.
The 2009 Mw 6.3 L’Aquila event caused extensive damage in the city of L’Aquila and in some small towns in its vicinity. The most severe damage was recognized SE of L’Aquila town along the Aterno river valley. Although building vulnerability and near-source effects are strongly responsible for the high level of destruction, site effects have been invoked to explain the damage heterogeneities and the similarities between the 2009 macroseismic field with the intensities of historical earthquakes. The small village of Onna is settled on quaternary alluvium and suffered during the L’Aquila event an extremely heavy damage in the masonry structures with intensity IX–X on the Mercalli-Cancani-Sieberg (MCS) scale. The village of Monticchio, far less than 1.3 km from Onna, is mostly situated on Mesozoic limestone and suffered a smaller level of damaging (VI MCS). In the present paper, we analyze the aftershock recordings at seismic stations deployed in a small area of the middle-Aterno valley including Onna and Monticchio. The aim is to investigate local amplification effects caused by the near-surface geology. Because the seismological stations are close together, vulnerability and near-source effects are assumed to be constant. The waveform analysis shows that the ground motion at Onna is systematically characterized by large high-frequency content. The frequency resonance is varying from 2 to 3 Hz and it is related to alluvial sediments with a thickness of about 40 m that overlay a stiffer Pleistocene substrate. The ground motion recordings of Onna are well reproduced by the predictive equation for the Italian territory.  相似文献   

16.
We present a fresh look at the source region of the 22 January 2003 M w 7.4 Armería earthquake, which occurred off the Pacific coast of the state of Colima, Mexico, near the town of Armería. The effects of this earthquake in the neighboring states of Colima and Jalisco were different and stronger than those of previous recent major earthquakes in the region. This earthquake and its aftershocks were recorded by two local telemetered seismograph networks (RESCO and RESJAL). From 22 January to 24 January 2003, no important seismicity was located on the plates interface, or within the Rivera Plate, and most epicenters were located west of the Armería River, which is the western border of the Colima Graben, and is located outside of the Colima Gap region. From 24 January to 31 January, the seismicity recorded by both networks showed a migration in depth, with an almost vertical offshore distribution between 4 and 24?km in depth. For this period, a seven-station portable digital seismograph network, equipped with three-component seismometers, was deployed in the epicentral area to study the aftershock sequence in detail. With this denser network more than 200 M L?>?2.0 aftershocks were recorded. The aftershock foci were deeper than those recorded during the early period and most of them locate on a hypothetical 12° dipping interface between the Rivera and North American Plates. Composite focal mechanism solutions for the aftershocks located during both periods indicate a reverse fault character that changes with time. Analysis of the new dataset still indicates that the earthquake was a shallow intraplate event.  相似文献   

17.
Newly identified ??a?? lava flows outcrop intermittently over an area of ~110?km2 in the western Deccan Volcanic Province (DVP), India. They occur in the upper Thakurvadi Formation in the region south of Sangamner. The flows, one of which is compound, are 15?C25?m thick, and exhibit well-developed basal and flow-top breccias. The lavas have microcrystalline groundmasses and are porphyritic or glomerocrystic and contain phenocrysts of olivine, clinopyroxene or plagioclase feldspar. They are chemically similar to compound p??hoehoe flows at a similar stratigraphic horizon along the Western Ghats. Petrographic and geochemical differences between ??a?? flows at widely spaced outcrops at the same stratigraphic horizon suggest that they are the product of several eruptions, potentially from different sources. Their presence in the DVP could suggest relative proximity to vents. This discovery is significant because ??a?? lavas are generally scarce in large continental flood basalt provinces, which typically consist of numerous inflated compound p??hoehoe lobes and sheet lobes. Their scarcity is intriguing, and may relate to either their occurrence only in poorly preserved or exposed proximal areas or to the flat plateau-like topography of flood basalt provinces that may inhibit channelization and ??a?? formation, or both. In this context, the ??a?? flow fields described here are inferred to be the products of eruptions that produced unusually high-effusion-rate lavas compared to typical flood basalt eruptions. Whether these phases were transitional to lower intensity, sustained eruptions that fed extensive low effusion rate p??hoehoe flow fields remains unclear.  相似文献   

18.
The strong ground motion prediction method ??Recipe?? was published by the Headquarters for Earthquake Research Promotion (HERP) of Japan. HERP has applied this method to prepare shaking maps for scenario earthquakes in specific active faults. Recently, Recipe was updated following its verification by simulations of strong ground motions associated with the Mw?=?6.6 off-shore earthquake west of Fukuoka prefecture in 2005, which occurred in the northwest part of the Kego fault zone located in northern Kyushu, Japan. One of the prominent changes in the upgraded version of Recipe is the inclusion of a procedure to evaluate seismic intensities on the ground surface from waveforms of S-wave velocity of 400?m/s on the engineering bedrock. By applying the upgraded version of Recipe, we have made shaking-maps for earthquakes in the southeast part of the Kego fault zone, which is located directly below the mega-city of Fukuoka. We assume four source models for scenario earthquakes; the locations of the asperities and the hypocenters vary between the models. The results show that in all cases, disastrous seismic intensities can strike a wide area of Fukuoka city. Differences in the distributions of seismic intensities among the four cases can be clearly observed in the area located on the extension of the source fault. Furthermore, we construct a velocity-layer structure model on the engineering bedrock for the central area of Fukuoka city. We assess not only the distribution of seismic intensities but also waveforms on the ground by using an equivalent linear method for the central area of Fukuoka city.  相似文献   

19.
Following the April 6th, 2009 Abruzzo mainshock, the Italian Civil Protection Department promoted a multidisciplinary study aimed at developing seismic microzonation maps for post-earthquake reconstruction planning. In the framework of this project, a Working Group, including the authors, was assembled to carry out a microzonation study on six villages located in the Middle Aterno valley. This paper focuses on the villages of Castelnuovo and Poggio Picenze, which experienced MCS intensity values of IX–X and VIII–IX, respectively. 1D and 2D linear equivalent site response analyses were carried out on representative geological cross-sections through the damaged centres and the expansion zones. The subsoil models resulting from geological, geotechnical and geophysical investigations were calibrated by comparing numerical amplification functions, in the linear range, with horizontal-to-vertical spectral ratio derived from both aftershocks and noise recordings. The input motions adopted for the analyses were five artificial accelerograms compatible with three response spectra obtained from the Italian seismic code, as well as from ad hoc probabilistic and deterministic studies. The results were expressed in the form of horizontal profiles of amplification factors in terms of peak ground acceleration, FPGA, as well as of the Housner intensity, FH, in two different range of periods; this latter parameter was shown to be almost independent of the input motion and allowed to express the dependency of site amplification on the frequency range. The amplification factors computed along the representative geological sections were finally extended with a rational procedure to the surrounding areas to draw Grade-3 microzonation maps.  相似文献   

20.
  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号