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1.
Bucharest is one of the cities most affected by earthquakes in Europe. Situated at 150–170 km distance from Vrancea epicentral zone, Bucharest had suffered many damages due to high energy Vrancea intermediate-depth earthquakes. For example, the 4 March 1977 event produced the collapse of 32 buildings with 8–12 levels, while more than 150 old buildings with 6–9 levels were seriously damaged. The studies done after this earthquake had shown the importance of the surface geological structure upon ground motion parameters. New seismic measurements are performed in Bucharest area aiming at defining better elastic and dynamic properties of the shallow sedimentary rocks. Down-hole seismic measurements were performed in a number of 10 cased boreholes drilled in the Bucharest City area. Processing and interpretation of the data lead to the conclusion that shallow sedimentary rocks can be considered weak in the area, down to 150–200 m depth. Seismic wave velocity values and bulk density values presented in the paper associated with local geology are useful primary data in the seismic microzonation of Bucharest City. They are used as 1D models to derive transfer functions and response spectra for the stack of sedimentary rocks in several parts of Bucharest area, leading to a better knowledge of the local site amplification and associated frequency spectra. In a recent study the H/V spectral ratio using Nakamura’s method was applied on the seismic noise measurements in 22 sites in Bucharest City in order to derive the fundamental period associated with these sites. The values confirm the previous results, showing a dominant resonance in the period range of 1.25–1.75 s. The fundamental periods obtained with Nakamura’s method are in good agreement with those computed on the basis of geological and geotechnical data in boreholes, which show an increase of the fundamental period in the Bucharest area from south to north, in the same direction as the increase of the thickness of the Quaternary deposits above the Fratesti layer which is considered the bedrock in the area.  相似文献   

2.
Vrancea major intermediate-depth earthquakes produced extreme damage in Bucharest city, located at about 165 km epicenter distance. Our purpose is to investigate the influence of local geological conditions upon the seismic motion in Bucharest in case of large (M>7) Vrancea earthquakes. Two input data sets are used: (a) geological, geotechnical and geophysical information, including in situ measurements, and (b) acceleration recordings of Vrancea earthquakes. Local response evaluation based on first dataset is confirmed by the spectral analysis of the earthquake records. Two main features are outlined: non-stationarity of ground motion dynamic amplification from one event to other and inadequacy of limiting the investigation depth to uppermost 30 m to evaluate ground dynamic characteristics. Consequently (1) we cannot extrapolate the ground motion response determined for moderate and small earthquakes to anticipate the effects of the large Vrancea shocks and (2) the local response is controlled by the entire package of Quaternary deposits which are significantly deeper than 30 m depth beneath Bucharest Area.  相似文献   

3.
A new prototype system for earthquake early warning in Taiwan   总被引：1，自引：0，他引：1  
A new prototype earthquake early warning (EEW) system is being developed and tested using a real-time seismographic network currently in operation in Taiwan. This system is based on the Earthworm environment which carries out integrated analysis of real-time broadband, strong-motion and short-period signals. The peak amplitude of displacement in the three seconds after the P arrival, dubbed Pd, is used for the magnitude determination. Incoming signals are processed in real time. When a large earthquake occurs, P-wave arrival times and Pd will be estimated for location and magnitude determinations for EEW purpose. In a test of 54 felt earthquakes, this system can report earthquake information in 18.8±4.1 s after the earthquake occurrence with an average difference in epicenter locations of 6.3±5.7 km, and an average difference in depths of 7.9±6.6 km from catalogues. The magnitudes approach a 1:1 relationship to the reported magnitudes with a standard deviation of 0.51. Therefore, this system can provide early warning before the arrival of S-wave for metropolitan areas located 70 km away from the epicenter. This new system is still under development and being improved, with the hope of replacing the current operational EEW system in the future.  相似文献   

4.
2021年5月22日2时4分青海省玛多县发生M7.4地震。四川地震预警台网成功地处理并产出了本次地震预警结果。本文针对四川地震预警系统产出的8次地震预警处理结果及预警减灾效能进行了分析。此次地震震中距四川地震预警网55km,首台触发后12.19s发布首次预警处理结果,前5次预警处理结果用时距离首台触发时间均小于35s。与正式地震目录对比,第1次预警处理结果震中位置偏差为17.1km,震级偏差为-1.8,盲区半径为121km。随着参与计算台站数量增多,震中位置偏差和震级偏差不断减小,盲区半径不断增大。由于地震破裂时间长和台站限幅等原因,8次预警震级均偏小。本次地震预警的有效获益区为震中距121～324km的环形区域,此区域内减灾效能显著。本次地震预警结果表明,四川地震预警系统在本次地震中预警产出效果较好,对于网外大地震预警有重要参考意义。  相似文献   

5.
On March 4, 1977, an earthquake with a moment magnitude M w 7.4 at a hypocentral depth of 94 km hit the Vrancea region (Romania). In Bucharest alone, the earthquake caused severe damage to 33,000 buildings while 1,424 people were killed. Under the umbrella of the SAFER project, the city of Bucharest, being one of the larger European cities at risk, was chosen as a test bed for the estimation of damage and connected losses in case of a future large magnitude earthquake in the Vrancea area. For the conduct of these purely deterministic damage and loss computations, the open-source software SELENA is applied. In order to represent a large event in the Vrancea region, a set of deterministic scenarios were defined by combining ranges of focal parameters, i.e., magnitude, focal depth, and epicentral location. Ground motion values are computed by consideration of different ground motion prediction equations that are believed to represent earthquake attenuation effects in the region. Variations in damage and loss estimates are investigated through considering different sets of building vulnerability curves (provided by HAZUS-MH and various European authors) to characterize the damaging behavior of prevalent building typologies in the city of Bucharest.  相似文献   

6.
PRESTo (PRobabilistic and Evolutionary early warning SysTem) is a software platform for regional earthquake early warning that integrates recently developed algorithms for real-time earthquake location and magnitude estimation into a highly configurable and easily portable package. The system is under active experimentation in Southern Italy on the Irpinia Seismic Network (ISNet), which is deployed in a seismogenic area that is expected to produce a large earthquake within the next 20 years. In this paper we describe the architecture of the system and test its performances using both small earthquakes (M<3.5) recorded at the ISNet and a large event recorded in Japan, through a simulation mode. The results show that, when a dense seismic network is deployed in the fault area, PRESTo can produce reliable estimates of earthquake location and size within 5–6 s from the event origin. Each estimate is provided as a probability density function, with an uncertainty that typically decreases with time: a stable solution is generally reached within 10 s from the origin.  相似文献   

7.
The earthquake risk on Romania is one of the highest in Europe, and seismic hazard for almost half of the territory of Romania is determined by the Vrancea seismic region, which is situated beneath the southern Carpathian Arc. The region is characterized by a high rate of occurrence of large earthquakes in a narrow focal volume at depth from 70 to 160 km. Besides the Vrancea area, several zones of shallow seismicity located within and outside the Romanian territory are considered as seismically dangerous. We present the results of probabilistic seismic hazard analysis, which implemented the “logic tree” approach, and which considered both the intermediate-depth and the shallow seismicity. Various available models of seismicity and ground-motion attenuation were used as the alternative variants. Seismic hazard in terms of macroseismic intensities, peak ground acceleration, and response spectra was evaluated for various return periods. Sensitivity study was performed to analyze the impact of variation of input parameters on the hazard results. The uncertainty on hazard estimates may be reduced by better understanding of parameters of the Vrancea source zone and the zones of crustal seismicity. Reduction of uncertainty associated with the ground-motion models is also very important issue for Romania.  相似文献   

8.
Bucharest, capital of Romania, is one of the most exposed big cities in Europe to seismic damage, due to the intermediate-depth earthquakes in the Vrancea region, to the vulnerable building stock and local soil conditions.This paper tries to answer very important questions related to the seismic risk at city scale that were not yet adequately answered. First, we analyze and highlight the bottlenecks of previous risk-related studies. Based on new researches in the hazard of Bucharest (recent microzonation map and ground-motion prediction equations, reprocessed real recorded data) and in vulnerability assessment (analytical methods, earthquake loss estimation software like SELENA and ELER, the recently implemented Near Real-Time System for Estimating the Seismic Damage in Romania) we provide an improved estimation of the number of buildings and population that could be affected, for different earthquake scenarios. A new method for enhancing the spatial resolution of the building stock data is used successfully.  相似文献   

9.
地震预警系统需要在破坏性的地震波到来前快速估算地震参数和地震动参数,以对可能出现的地震灾害进行预测,对重要工程、人员密集区域发布警报信息.以Pd估测PGV的方法是地震预警研究涉及的一种重要问题,该方法利用初至P波触发后前几秒的峰值位移(Pd)对最终地震动峰值速度(PGV)进行估算,以满足预警的需要.本文对2016年在日本发生的熊本地震及其前震、余震的震中距100km以内、矩震级大于4级、井下基岩PGA5cm·s~(-2)和地表PGA20cm·s~(-2)的Kik-net强地震动记录进行处理分析,用于研究以Pd估测PGV的方法.将获得的强地震动数据按震中距从0~100km平均划分为5个区段,在记录时间3~10s范围内将Pd的计算取8个时间窗,分别对每个震中距区段、每一个Pd的时间窗下的PGV-Pd数据进行线性拟合,最终提出了一套应对不同震中距对位移幅值连续追踪测定PGV的算法.对每一个震中距区段的研究表明,震中距会对PGV-Pd关系产生影响.对5次地震进行验证分析,认为基于基岩记录估测基岩PGV的准确度高于基于地表记录估测地表PGV的准确度;对震中距进行分段的PGV估测方法准确度高于不考虑震中距因子的估测方法.最后拓展了将井下基岩Pd估测井下基岩PGV这种原地地震预警方法,使其能够为异地P波预警方法服务.  相似文献   

10.
The paper presents recent achievements in evaluations of site-dependent seismic hazard in Romania and the capital city of Bucharest caused by the Vrancea focal zone (SE-Carpathians). The zone is characterized by a high rate of occurrence of large earthquakes in a narrow focal volume at depths 60–170 km. The database that was used for the hazard evaluation includes parameters of seismicity, ground-motion source scaling and attenuation models (Fourier amplitude spectra), and site-dependent spectral amplification functions. Ground-motion characteristics were evaluated on the basis of several hundred records from more than 120 small magnitude (M 3.5–5) earthquakes occurred in 1996–2001 and a few tens of acceleration records obtained during four large (M 7.4, 7.2, 6.9 and 6.3) earthquakes. The data provide a basis for probabilistic seismic hazard assessment in terms of peak ground acceleration, peak spectral acceleration and MSK intensity using Fourier amplitude spectra for various exceedance probabilities or average return periods. It has been shown that the influence of geological factors plays very important role in distribution of earthquake ground-motion parameters along the territory of Romania.  相似文献   

11.
We study the influence of different source characteristics (depth, distance, type and azimuth) on the site effect in Acapulco and the Valley of Mexico. Site amplification was estimated by means of spectral ratios (both horizontal-to-vertical spectral ratio and standard spectral ratio techniques were applied) from earthquake recordings at soft and hard sites. In Acapulco, 125 Mexican earthquakes covering a hypocentral range of 7–290 km and a depth range (H) of 3–61 km were analyzed in three different groups of hypocentral distances. In the Valley of Mexico, we estimate site effect at five locations using recordings from shallow-coastal interplate (200?Δ?570 km; H?35 km) and normal-faulting, intermediate-depth inslab (132?Δ?738 km; 32?H?178 km) earthquakes, as well as from teleseismic events. Our results seem to point to negligible dependence of site effects on the source location and type.  相似文献   

12.
The paper presents results of studying the attenuation of ground accelerations from earthquakes of the Vrancea with magnitudes less that 6.0 at distance greater than 300 km in a narrow sector located northeast of the focal region, within the limits of which are located acting and planned nuclear power plants (NNPs). Attenuation of peak ground accelerations in individual sections along the Vrancea–IRIS OBN station path is approximated by individual functions. It is shown that for a rough estimation of the seismic effect of earthquakes from the Vrancea zone it is acceptable to use the empirical relationship obtained by F.F. Aptikaev. For a more accurate estimate, it needs to be modified by adding a constant, whose value depends on the specific conditions of the NPP sites. It is shown that the results of data analysis on moderate earthquakes can be extrapolated to an earthquake with the maximum possible magnitude for the Vrancea zone and used to estimate the maximum seismic effects at the sites of operating and planned NPPs.  相似文献   

13.
—?The mapping of the seismic ground motion in Bucharest, due to the strong Vrancea earthquakes, is carried out using a complex hybrid waveform modeling method that allows easy parametric tests. Starting from the actually available strong motion database, we can make realistic predictions for the possible ground motion. The basic information necessary for the modeling consists of: (a) The representative mechanisms for the strong subcrustal events, (b) the average regional structural model, and (c) the local structure for Bucharest. Two scenario earthquakes are considered and the source influence on the local response is analyzed in order to define generally valid ground motion parameters, to be used in the seismic hazard estimations. The source has its own (detectable) contribution on the ground motion and its effects on the local response in Bucharest are quite stable on the transversal component (T), while the radial (R) and vertical (V) components are sensitive to the scenario earthquake. Although the strongest local effects affect the T component, both observed and synthetic, a complete determination of the seismic input for the built environment requires the knowledge of all three components of motion (R, V, T). The damage observed in Bucharest for the March 4, 1977 Vrancea event, the strongest earthquake to strike the city in modern times, is in agreement with the synthetic signals and local response.  相似文献   

14.
2020年7月12日,河北唐山发生MS5.1地震,河北省地震预警系统成功地处理并产出了这次地震预警各种结果数据,本文借助此次地震对河北地震预警网内震中距200km范围内台站产出质量以及地震预警前5次处理结果进行详细分析。此次地震发生在河北地震预警网内,平均台间距为10km,首台触发后3s、震后6s发布首次处理结果,与编目结果相比,震级偏差为-1.3,震中位置偏差为2.6km,盲区半径为18km。随着参与定位台站数量增多,震级与位置偏差越来越小,但震级仍整体偏小。河北地震预警网台站产出质量整体较高,其中烈度台作为地震预警最重要的组成部分,是决定预警效果的关键因素。本次地震震中距200km范围内,烈度台平均信噪比为48,震中距50km范围内平均信噪比为112,符合预警系统对信噪比的要求。本次地震预警结果表明,河北地震预警网内台站布局基本合理,波形质量较高,地震预警系统处理软件在本次地震中预警产出效果较好,已经具备了一定的地震预警能力。  相似文献   

15.
According to general seismic zoning maps, Moscow is in an area with a seismic intensity of 5, in which the maximum seismic effect is expected from remote deep-focal earthquakes in the Vrancea zone (Eastern Carpathians, Romania). In our previous studies, an earthquake with a hypocenter at a depth of 80–150 km in the Vrancea zone, a moment magnitude of Mw = 8.0, and a drop in stress of Δσ = 325 bar was used as a scenario earthquake for Moscow. A series of model acceleration time histories for ground vibrations was calculated for this earthquake for the reference local conditions of the Moskva seismic station (Moscow, Pyzhevskii per. 3). In this paper, these acceleration time histories are used to calculate the acceleration time histories and estimate the ground vibration parameters for an scenario earthquake at other sites on the territory of Moscow for which information on soil conditions is available. Since the epicentral distance is large (~1300 km), it can be assumed that changes in the shape and spectral content of the acceleration time histories at different sites in Moscow are only caused by different local conditions.  相似文献   

16.
In this study, the attenuation properties of the crust and the quality factor of S wave in eastern Anatolia (Turkey) were determined by local earthquakes for two different areas, Oltu and Erzurum. Seismic wave attenuation can be changed with high pressure or structural effects. Therefore, we argued that the estimation of attenuation coefficient in seismic active zones in Eastern Anatolia is a very useful tool to determine seismic activities. It uses regional waveform data set from two stations, OLT and ERZ, for 95 events that occurred in these regions between 2001 and 2005. The attenuation has been determined using the Chobra–Alexeev model based on the epicenter distance–amplitude relations. This model allows for investigation of the effects of variations in attenuation properties for different areas. We introduced a new magnitude formula for these areas using the amplitude normalization methods for reference values ML=4, so as to correct effects of the magnitudes. We also determined velocity of seismic waves. The average attenuation coefficient (α), average quality factor (Qs) and P and S waves velocities were obtained with normalized amplitude values for Erzurum (ERZ) and Oltu (OLT) as 0.0135 km−1, 37, 6.20 km/s and 3.38 km/s and 0.0151, 34, 6.13 and 3.48.  相似文献   

17.
The three-dimensional P-wave velocity structure beneath the Katmai group of volcanoes is determined by inversion of more than 10,000 rays from over 1000 earthquakes recorded on a local 18 station short-period network between September 1996 and May 2001. The inversion is well constrained from sea level to about 6 km below sea level and encompasses all of the Katmai volcanoes; Martin, Mageik, Trident, Griggs, Novarupta, Snowy, and Katmai caldera. The inversion reduced the average RMS travel-time error from 0.22 s for locations from the standard one-dimensional model to 0.13 s for the best three-dimensional model. The final model, from the 6th inversion step, reveals a prominent low velocity zone (3.6–5.0 km/s) centered at Katmai Pass and extending from Mageik to Trident volcanoes. The anomaly has values about 20–25% slower than velocities outboard of the region (5.0–6.5 km/s). Moderately low velocities (4.5–6.0 km/s) are observed along the volcanic axis between Martin and Katmai Caldera. Griggs volcano, located about 10 km behind (northwest of) the volcanic axis, has unremarkable velocities (5.0–5.7 km/s) compared to non-volcanic regions. The highest velocities are observed between Snowy and Griggs volcanoes (5.5–6.5 km/s). Relocated hypocenters for the best 3-D model are shifted significantly relative to the standard model with clusters of seismicity at Martin volcano shifting systematically deeper by about 1 km to depths of 0 to 4 km below sea level. Hypocenters for the Katmai Caldera are more tightly clustered, relocating beneath the 1912 scarp walls. The relocated hypocenters allow us to compare spatial frequency-size distributions (b-values) using one-dimensional and three-dimensional models. We find that the distribution of b is significantly changed for Martin volcano, which was characterized by variable values (0.8 < b < 2.0) with standard locations and more uniform values (0.8 < b < 1.2) after relocation. Other seismic clusters at Mageik (1.2 < b < 2.2), Trident (0.5 < b < 1.5) and Katmai Caldera (0.8 < b < 1.8) had stable b-values indicating the robustness of the observations. The strong high b-value region at Mageik volcano is mainly associated with an earthquake swarm in October, 1996 that possibly indicates a shallow intrusion or influx of gas. The new velocity and spatial b-value results, in conjunction with prior gravity (Bouguer anomalies up to − 40 mgal) and interferometry (several cm uplift) data, provide strong evidence in favor of partially molten rock at shallow depths beneath the Mageik–Katmai–Novarupta region. Moderately low velocities beneath Martin and Katmai suggest that old, mostly solidified intrusions exist beneath these volcanoes. Higher relative velocities beneath the Griggs and Snowy vents suggest that no magma is resident in the shallow crust beneath these volcanoes.  相似文献   

18.
On October 27, 2004, a moderate size earthquake occurred in the Vrancea seismogenic region (Romania). The Vrancea seismic zone is an area of concentrated seismicity at intermediate depths beneath the bending area of the southeastern Carpathians. The 2004 M w?=?6 Vrancea subcrustal earthquake is the largest seismic event recorded in Romania since the 1990 earthquakes. With a maximum macroseismic intensity of VII Medvedev–Sponheuer–Kárník (MSK-64) scale, the seismic event was felt to a distance of 600 km from the epicentre. This earthquake caused no serious damage and human injuries. The main purpose of this paper is to present the macroseismic map of the earthquake based on the MSK-64 intensity scale. After the evaluation of the macroseismic effects of this earthquake, an intensity dataset has been obtained for 475 sites in the Romanian territory. Also, the maximum horizontal accelerations recorded in the area by the K2 network are compared to the intensity values.  相似文献   

19.
Inflation along Kilauea's Southwest Rift Zone in 2006   总被引：1，自引：0，他引：1  
We report on InSAR and GPS results showing the first crustal inflation along the southwest rift zone at Kilauea volcano in over 20 years. Two independent interferograms (May 2–August 2, 2006 and June 22–Nov 7, 2006) from the ALOS PALSAR instrument reveal domal uplift located southwest of the main caldera. The uplift is bounded on the northeast by the caldera and follows the southwest rift zone for about 12 km. It is approximately 8 km wide. We use data derived from permanent GPS stations to calibrate the InSAR displacement data and estimate uplift of 7.7 cm during the first interferogram and 8.9 cm during the second with line-of-sight volumes of 2.8 × 106 m3 and 3.0 × 106 m3 respectively. The earthquake record for the periods before, during, and after inflation shows that a swarm of shallow earthquakes (z < 5 km) signaled the beginning of the uplift and that elevated levels of shallow seismicity along the rift zones occurred throughout the uplift period. GPS data indicate that the inflation occurred steadily over nine months between mid-January and mid-October, 2006 making injection of a sill unlikely. We attribute the inflation to recharge of a shallow ductile area under the SWRZ.  相似文献   

20.
We report results from a detailed study of seismicity in central Kamchatka for the period from 1960 to 1997 using a modified traditional approach. The basic elements of this approach include (a) segmentation of the seismic region concerned (the Kronotskii and Shipunskii geoblocks, the continental slope and offshore blocks), (b) studying the variation in the rate of M = 4.5–7.0 earthquakes and in the amount of seismic energy release over time, (c) studying the seismicity variations, (d) separate estimates of earthquake recurrence for depths of 0–50 and 50–100 km. As a result, besides corroborating the fact that a quiescence occurred before the December 5, 1997, M = 7.9 Kronotskii earthquake, we also found a relationship between the start of the quiescence and the position of the seismic zone with respect to the rupture initiation. The earliest date of the quiescence (decreasing seismicity rate and seismic energy release) was due to the M = 4.5–7.0 earthquakes at depths of 0–100 km in the Kronotskii geoblock (8–9 years prior to the earthquake). The intermediate start of the quiescence was due to distant seismic zones of the Shipunskii geoblock and the circular zone using the RTL method, combining the Shipunskii and Kronotskii geoblocks (6 years). Based on the low magnitude seismicity (M≥2.6) at depths of 0–70 km in the southwestern part of the epicentral zone (50–100 km from the mainshock epicenter), the quiescence was inferred to have occurred a little over 3 years (40 months) before the mainshock time and a little over 2 years (25 months) in the immediate vicinity of the epicenter (0–50 km). These results enable a more reliable identification of other types of geophysical precursors during seismic quiescences before disastrous earthquakes.  相似文献   

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