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1.
Seismic hazard assessment of slow active fault zones is challenging as usually only a few decades of sparse instrumental seismic monitoring is available to characterize seismic activity. Tectonic features linked to the observed seismicity can be mapped by seismic imaging techniques and/or geomorphological and structural evidences. In this study, we investigate a seismic lineament located in the Swiss Alpine foreland, which was discussed in previous work as being related to crustal structures carrying in size the potential of a magnitude M 6 earthquake. New, low-magnitude (?2.0 ≤ ML ≤ 2.5) earthquake data are used to image the spatial and temporal distribution of seismogenic features in the target area. Quantitative and qualitative analyses are applied to the waveform dataset to better constrain earthquakes distribution and source processes. Potential tectonic features responsible for the observed seismicity are modelled based on new reinterpretations of oil industry seismic profiles and recent field data in the study area. The earthquake and tectonic datasets are then integrated in a 3D model. Spatially, the seismicity correlates over 10–15 km with a N–S oriented sub-vertical fault zone imaged in seismic profiles in the Mesozoic cover units above a major decollement on top of the mechanically more rigid basement and seen in outcrops of Tertiary series east of the city of Fribourg. Observed earthquakes cluster at shallow depth (<4 km) in the sedimentary cover. Given the spatial extend of the observed seismicity, we infer the potential of a moderate size earthquake to be generated on the lineament. However, since the existence of along strike structures in the basement cannot be excluded, a maximum M 6 earthquake cannot be ruled out. Thus, the Fribourg Lineament constitutes a non-negligible source of seismic hazard in the Swiss Alpine foreland.  相似文献   

2.
The thickness of the seismogenic layer is a key parameter for seismic hazard, since it can be used to constrain the maximum depth of faulting and the potential magnitude. In this study, we compute the seismogenic thickness in the Italian region by defining the lower seismicity cut‐off, using high‐quality hypocentral locations of earthquakes that occurred in the past decade. Along the eastern Alps, the seismogenic thickness is about 12–14 km, laterally homogeneous along the entire south‐verging thrust front. In the Apennines extensional belt, lateral changes in seismogenic thickness are evident, and correlate with changes in the seismic energy released by past earthquakes. The potential magnitude is larger in the southern Apennines where the seismogenic thickness is greater (16–18 km) than in the northern Apennines where it is less (6–10 km) and seismic energy is partially released by the creeping of faults.  相似文献   

3.
The cause for prolific seismicity in the Koyna region is a geological enigma. Attempts have been made to link occurrence of these earthquakes with tectonic strain as well as the nearby reservoirs. With a view to providing reliable seismological database for studying the earth structure and the earthquake process in the Koyna region, a state of the art digital seismic network was deployed for twenty months during 1996–97. We present preliminary results from this experiment covering an area of 60 × 80 km2 with twenty seismic stations. Hypocentral locations of more than 400 earthquakes confined to 11×25 km2 reveal fragmentation in the seismicity pattern — a NE — SW segment has a dip towards NW at approximately 45°, whilst the other two segments show a near vertical trend. These seismic segments have a close linkage with the Western Ghat escarpment and the Warna fault. Ninety per cent of the seismicity is confined within the depth range of 3–10 km. The depth distribution of earthquakes delimits the seismogenic zone with its base at 10 km indicating a transition from an unstable to stable frictional sliding regime. The lack of shallow seismicity between 0 and 3 km indicates a mature fault system with well-developed gouge zones, which inhibit shallow earthquake nucleation. Local earthquake travel time inversion for P- and S-waves show ≈ 2% higher velocity in the seismogenic crust (0–10 km) beneath the epicentral tract relative to a lower velocity (2–3%) in the adjoining region. The high P- and S-wave velocity in the seismogenic crust argues against the presence of high pressure fluid zones and suggests its possible linkage with denser lithology. The zone of high velocity has been traced to deeper depths (≈ 70 km) through teleseismic tomography. The results reveal segmented and matured seismogenic fault systems in the Koyna region where seismicity is possibly controlled by strain build up due to competent lithology in the seismic zone with a deep crustal root.  相似文献   

4.
Advances in earthquake data acquisition and processing techniques have allowed for improved quantification of source parameters for local Australian earthquakes. Until recently, only hypocentral locations and local magnitudes (ML) had been determined routinely, with little attention given to the inversion of additional source parameters. The present study uses these new source data (e.g. seismic moment, stress drop, source dimensions) to further extend our understanding of seismicity and the continental stress regime of the Australian landmass and its peripheral regions.

Earthquake activity within Australia is typically low, and the proportion of small to large events (i.e. the b value) is also low. It is observed that average stress drops for southeastern Australian earthquakes appear to increase with seismic moment to relatively high levels, up to approximately 10 MPa for ML 5.0 earthquakes. This is thought to be indicative of high compressive crustal stress, coupled with strong rocks and fault asperities. Furthermore, the data indicates that shallow focus earthquakes (shallower than 6 km) appear to produce lower than average stress drops than deeper earthquakes (between 6 and 20 km) with similar moment.

Recurrence estimates were obtained for a discrete seismogenic zone in southeastern Australia. Decreasing b values with increasing focal depth for this zone indicate that larger earthquakes (with high stress drops) tend to occur deeper in the crust. This may offer an explanation for the apparent increase of stress drop with hypocentral depth. Consequently, earthquake hazard estimates that assume a uniform Gutenburg–Richter distribution with depth (i.e. constant b value) may be too conservative and therefore slightly overestimate seismic hazard for surface sites in southeastern Australia.  相似文献   


5.
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6.
东南亚地区是“21世纪海上丝绸之路”（以下简称“海洋丝路”）的重要组成部分,该区历史上曾发生十余次巨大地震,地震及其次生地质灾害是威胁东南亚地区经济社会发展和国际合作的主要自然灾害。系统梳理该区地震活动的时空分布特征及评估未来灾害风险格局,对于推进“一带一路”倡议实施及区域经济社会可持续发展具有重要意义。文章基于东南亚地区1900年以来M≥5地震的时空分布统计分析和地震b值计算,揭示出该区的地震活动在时间上表现出活跃期与平静期交替变化的特征;空间上表现出明显的聚集效应,成丛性强且主要集中在5个地震统计区内,其中印尼—马来多岛弧盆系地震区和菲律宾群岛地震区的地震活动最为活跃。总体而言,东南亚5个地震区的b值偏低,在0.42~0.91之间。该区内的地震b值也存在时空差异,受大地震事件、俯冲带年龄、活动断裂带和震源深度等众多因素影响,但主控因素在不同区域有所不同。地震b值时空变化特征对区域地震活动预测具有启示作用。上述认识为推进“海洋丝路”工程建设和“一带一路”防灾减灾对策提供了科学支撑。  相似文献   

7.
We present the estimated source parameters from SH-wave spectral modeling of selected 463 aftershocks (2002–06) of the 26 January 2001 Bhuj earthquake, the well-recorded largest continental intraplate earthquake. The estimated seismic moment (Mo), corner frequency (fc), source radius (r) and stress drop (Δσ) for aftershocks of moment magnitude 1.7 to 5.6 range from 3.55×1011 to 2.84×1017 N-m, 1.3 to 11.83 Hz, 107 to 1515 m and 0.13 to 26.7 MPa, respectively, while the errors in fc and Δσ are found to be 1.1 Hz and 1.1 MPa, respectively. We also notice that the near surface attenuation factor (k) values vary from 0.02 to 0.03. Our estimates reveal that the stress drop values show more scatter (Mo0.5 to 1 is proportional to Δσ) toward the larger Mo values (≥1014.5 N-m), while they show a more systematic nature (Mo3 is proportional to Δσ) for smaller Mo values (<1014.5 N-m), which can be explained as a consequence of a nearly constant rupture radius for smaller aftershocks in the region. The large stress drops (= 10 MPa) associated with events on the north Wagad fault (at 15–30 km depth) and Gedi fault (at 3–15 km depth) can be attributed to the large stress developed at hypocentral depths as a result of high fluid pressure and the presence of mafic intrusive bodies beneath these two fault zones.  相似文献   

8.
This article is to review results from scientific drilling and fault-zone trapped waves(FZTWs) at the south Longman-Shan fault(LSF) zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan, China. Immediately after the mainshock, two Wenchuan Fault Scientific Drilling(WFSD) boreholes were drilled at WFSD-1 and WFSD-2 sites approximately 400 m and 1 km west of the surface rupture along the Yinxiu-Beichuan fault(YBF), the middle fault strand of the south LSF zone. Two boreholes met the principal slip of Wenchuan earthquake along the YBF at depths of 589-m and 1230-m, respectively. The slip is accompanied with a 100-200-m-wide zone consisting of fault gouge, breccia, cataclasite and fractures. Close to WFSD-1 site, the nearly-vertical slip of ~4.3-m with a 190-m wide zone of highly fractured rocks restricted to the hanging wall of the YBF was found at the ground surface after the Wenchuan earthquake. A dense linear seismic array was deployed across the surface rupture at this venue to record FZTWs generated by aftershocks. Observations and 3-D finite-difference simulations of FZTWs recorded at this cross-fault array and network stations close to the YBF show a distinct low-velocity zone composed by severely damaged rocks along the south LSF at seismogenic depths. The zone is several hundred meters wide along the principal slip, within which seismic velocities are reduced by ~30–55% from wall-rock velocities and with the maximum velocity reduction in the ~200-m-wide rupture core zone at shallow depth. The FZTW-inferred geometry and physical properties of the south LSF rupture zone at shallow depth are in general consistent with the results from petrological and structural analyses of cores and well log at WFSD boreholes. We interpret this remarkable low-velocity zone as being a break-down zone during dynamic rupture in the 2008 M8 earthquake. We examined the FZTWS generated by similar earthquakes before and after the 2008 mainshock and observed that seismic velocities within fault core zone was reduced by ~10% due to severe damage of fault rocks during the M8 mainshock. Scientific drilling and locations of aftershocks generating prominent FZTWs also indicate rupture bifurcation along the YBF and the Anxian-Guangxian fault(AGF), two strands of the south LSF at shallow depth. A combination of seismic, petrologic and geologic study at the south LSF leads to further understand the relationship between the fault-zone structure and rupture dynamics, and the amplification of ground shaking strength along the low-velocity fault zone due to its waveguide effect.  相似文献   

9.

The 1979 Cadoux earthquake (magnitude Ms ～ 6.0), which caused over $4 million damage in 1979, occurred in the Southwest Seismic Zone (SWSZ) of Western Australia and produced a shallow dipping thrust fault with an average strike close to north‐south. The fault length was approximately 15 km and the maximum displacement close to 1 m. The seismic moment is estimated to be 1.8 ±0.1 X 1018 Nm and the earthquake was, like the 1968 Meckering earthquake, caused by east‐west compressive stress in the crust. Aftershocks of the Cadoux earthquake are still continuing (1986) at the northern and southern ends of the area affected by the main earthquake; strain‐release data from the aftershocks indicate that significant strain energy is yet to be released in the region. Overcoring measurements in the SWSZ indicated high stress (up to 30 MPa) at shallow depths (～ 10 m). Near the epicentre of the Cadoux earthquake overcoring measurements revealed stress levels ranging from about 4 MPa, less than 1 km from the fault trace, to about 20 MPa at 15 km from the fault. This difference in stress at the two locations is much larger than the stress drop associated with the Cadoux earthquake (～ 1 MPa) obtained from seismological observations. However, the maximum compressive stress direction is consistent with the direction of the P‐axis obtained from the focal mechanism. Reliable hydro fracturing results, from a depth of 65 m, were similar to the stress directions and magnitudes obtained from overcoring measurements made at the same site. It appears that the crust in the SWSZ is under compressive stress and that earthquake activity releases this stress in small areas rather than along linear fault zones. Shallow earthquakes of similar magnitude could well take place in the SWSZ during the next 50 years.  相似文献   

10.
The epicentral tract of the great Assam earthquake of 1897 of magnitude 8·7 was monitored for about 6 months using an array of portable seismographs. The observed seismicity pattern shows several diversely-oriented linear trends, some of which either encompass or parallel known geological faults. A vast majority of the recorded micro-earthquakes had estimated focal depths between 8–14 km. The maximum estimated depth was 45 km. On the basis of a seismic velocity model for the region reported recently and these depth estimates we suggest that the rupture zone of the great 1897 earthquake had a depth of 11–12 km under the western half of the Shillong massif. Four composite fault plane solutions define the nature of dislocation in three of the seismic zones. Three of them show oblique thrusting while one shows pure dip slip reverse faulting. The fault plane solutions fit into a regional pattern of a belt of earthquakes extending in NW-SE direction across the north eastern corner of the Bengal basin. The maximum principle stress axis is approximately NS for all the solutions in conformity with the inferred direction of the Indian-EuroAsian plate convergence in the eastern Himalaya.  相似文献   

11.
We performed a probabilistic analysis of earthquake hazard input parameters, NW Turkey covers Gelibolu and Biga Peninsulas, and its vicinity based on four seismic sub-zones. The number of earthquakes with magnitude M ≥ 3.0 occurred in this region for the period between 1912 and 2007 is around 5130. Four seismic source sub-zones were defined with respect to seismotectonic framework, seismicity and fault geometry. The hazard perceptibility characterization was examined for each seismic source zone and for the whole region. The probabilities of earthquake recurrences were obtained by using Poisson statistical distribution models. In order to determine the source zones where strong and destructive earthquakes may occur, distribution maps for a, b and a/b values were calculated. The hazard scaling parameters (generally known as a and b values) in the computed magnitude–frequency relations vary in the intervals 4.28–6.58 and 0.59–1.13, respectively, with a RMS error percentage below 10 %. The lowest b value is computed for sub-zone three indicating the predominance of large earthquakes mostly at Gelibolu (Gallipoli) and north of Biga Peninsula (southern Marmara region), and the highest b value is computed for sub-zone two Edremit Bay (SW Marmara region). According to the analysis of each seismic sub-zone, the greatest risk of earthquake occurrence is determined for the triangle of Gelibolu–Tekirda? western part of Marmara Sea. Earthquake occurrence of the largest magnitude with 7.3 within a 100-year period was determined to be 46 % according to the Poisson distribution, and the estimated recurrence period of years for this region is 50 ± 12. The seismic hazard is pronounced high in the region extending in a NW–SE direction, north of Edremit Bay, west of Saros Bay and Yenice Gönen (southern Marmara region) in the south. High b values are generally calculated at depths of 5–20 km that can be expressed as low seismic energy release and evaluated as the seismogenic zone.  相似文献   

12.
Temporary local seismic networks were installed in western Crete, in central Crete, and on the island Gavdos south of western Crete, respectively, in order to image shallow seismically active zones of the Hellenic subduction zone.More than 4000 events in the magnitude range between −0.5 and 4.8 were detected and localized. The resulting three-dimensional hypocenter distribution allows the localization of seismically active zones in the area of western and central Crete from the Mediterranean Ridge to the Cretan Sea. Furthermore, a three-dimensional structural model of the studied region was compiled based on results of wide-angle seismics, surface wave analysis and receiver function studies. The comparison of the hypocenter distribution and the structure has allowed intraplate and interplate seismicity to be distinguished.High interplate seismicity along the interface between the subducting African lithosphere and the Aegean lithosphere was found south of western Crete where the interface is located at about 20 to 40 km depth. An offset between the southern border of the Aegean lithosphere and the southern border of active interplate seismicity is observed. In the area of Crete, the offset varies laterally along the Hellenic arc between about 50 and 70 km.A southwards dipping zone of high seismicity within the Aegean lithosphere is found south of central Crete in the region of the Ptolemy trench. It reaches from the interface between the plates at about 30 km depth towards the surface. In comparison, the Aegean lithosphere south of western Crete is seismically much less active including the region of the Ionian trench. Intraplate seismicity within the Aegean plate beneath Crete and north of Crete is confined to the upper about 20 km. Between 20 and 40 km depth beneath Crete, the Aegean lithosphere appears to be seismically inactive. In western Crete, the southern and western borders of this aseismic zone correlate strongly with the coastline of Crete.  相似文献   

13.
This paper examines the variability of seismic activity observed in the case of different geological zones of peninsular India (10°N–26°N; 68°E–90°E) based on earthquake catalog between the period 1842 and 2002 and estimates earthquake hazard for the region. With compilation of earthquake catalog in terms of moment magnitude and establishing broad completeness criteria, we derive the seismicity parameters for each geologic zone of peninsular India using maximum likelihood procedure. The estimated parameters provide the basis for understanding the historical seismicity associated with different geological zones of peninsular India and also provide important inputs for future seismic hazard estimation studies in the region. Based on present investigation, it is clear that earthquake recurrence activity in various geologic zones of peninsular India is distinct and varies considerably between its cratonic and rifting zones. The study identifies the likely hazards due to the possibility of moderate to large earthquakes in peninsular India and also presents the influence of spatial rate variation in the seismic activity of this region. This paper presents the influence of source zone characterization and recurrence rate variation pattern on the maximum earthquake magnitude estimation. The results presented in the paper provide a useful basis for probabilistic seismic hazard studies and microzonation studies in peninsular India.  相似文献   

14.
Northeastern Brazil is, within the present knowledge of historical and instrumental seismicity, one the most seismic active areas in intraplate South America. Seismic activity in the region has occurred mainly around the Potiguar basin. This seismicity includes earthquake swarms characterized by instrumentally-recorded events ≤ 5.2 mb and paleoseismic events ≥ 7.0. Our study concentrates in the João Câmara (JC) epicentral area, where an earthquake swarm composed of more than 40,000 aftershocks occurred mainly from 1986 to 1990 along the Samambaia fault; 14 of which had mb > 4.0 and two of which had 5.1 and 5.0 mb. We describe and compare this aftershock sequence with the present-day stress field and the tectonic fabric in an attempt to understand fault geometry and local control of seismogenic faulting. Earthquake data indicate that seismicity decreased steadily from 1986 to 1998. We selected 2,746 epicenters, which provided a high-quality and precise dataset. It indicates that the fault trends 37° azimuth, dips 76°–80° to NW, and forms an alignment  27 km long that cuts across the NNE–SSW-trending ductile Precambrian fabric. The depth of these events ranged from  1 km to  9 km. The fault forms an echelon array of three main left-bend segments: one in the northern and two in the southern part of the fault. A low-seismicity zone, which marks a contractional bend, occurs between the northern and southern segments. Focal mechanisms indicate that the area is under an E–W-oriented compression, which led to strike–slip shear along the Samambaia fault with a small normal component. The fault is at 53° to the maximum compression and is severely misoriented for reactivation under the present-day stress field. The seismicity, however, spatially coincides with a brittle fabric composed of quartz veins and silicified-fault zones. We conclude that the Samambaia fault is a discontinuous and reactivated structure marked at the surface by a well-defined brittle fabric, which is associated with silica-rich fluids.  相似文献   

15.
Characteristics of the seismicity in depth ranges 0–33 and 34–70 km before ten large and great (M w = 7.0−9.0) earthquakes of 2000–2008 in the Sumatra region are studied, as are those in the seismic gap zones where no large earthquakes have occurred since at least 1935. Ring seismicity structures are revealed in both depth ranges. It is shown that the epicenters of the main seismic events lie, as a rule, close to regions of overlap or in close proximity to “shallow” and “deep” rings. Correlation dependences of ring sizes and threshold earthquakes magnitudes on energy of the main seismic event in the ring seismicity regions are obtained. Identification of ring structures in the seismic gap zones (in the regions of Central and South Sumatra) suggests active processes of large earthquake preparation proceed in the region. The probable magnitudes of imminent seismic events are estimated from the data on the seismicity ring sizes.  相似文献   

16.
The aim of this study is to define the Vp and Vp/Vs structure of the fault zone ruptured by the ML 5.1 earthquake of October 15, 1996 which occurred near Reggio Emilia (central-northern Italy). A 1-month-long seismic sequence followed the mainshock and occurred in a small region along the outer border of the northern Apenninic belt, at depth ranging between 10 and 17 km. P- and S-wave arrival times from 304 aftershocks recorded by two local dense seismic arrays installed in the epicentral region have been inverted to obtain one- and three-dimensional velocity models by using state of the art local earthquake tomographic techniques. Velocity models and aftershock relocation help us to infer the seismotectonic of the region. Earthquakes originated along a NW-dipping backthrust of a NE-trending main thrust, composing the western part of the broad Ferrara Arc. A main high Vp and high Vp/Vs region delineates a pop-up structure in the center of the area. The high Vp/Vs within the pop-up structure supports the presence of a zone with increased pore pressure. The hypocentral depth of both mainshock and aftershocks is greater than those usually found for the main seismogenic regions of the Apenninic belt. P-wave velocity values in the seismogenic area, obtained by tomography, are compatible with rocks of the Mesozoic cover and suggest that seismicity occurred within the Mesozoic units stack at present by compressional tectonics.  相似文献   

17.
The paper presents a detailed analysis of 1st April 2015 earthquake, whose epicenter (30.16° N, 79.28° E) was located near Simtoli village of Chamoli district, Uttarakhand. The focal depth is refined to 7 km by the grid search technique using moment tensor inversion. The source parameters of the earthquake as estimated by spectral analysis method suggested the source radius of ~1.0 km, seismic moment as 1.99E+23 dyne-cm with moment magnitude (Mw) of 4.8 and stress drop of 69 bar. The fault plane solution inferred using full waveform inversion indicated two nodal planes, the northeast dipping plane having strike 334° and dip 5° and the southwest dipping plane with dip 86° and strike 118°. The parallelism of the nodal plane striking 334° with dip 5° as indicated in depth cross sections of the tectonic elements suggested the north dipping Main Boundary Thrust (MBT) to be the causative fault for this earthquake. Spatio-temporal distribution of earthquakes during the period 1960-2015 showed seismic quiescence during 2006-2010 and migration of seismicity towards south.  相似文献   

18.
Evidence of right‐lateral offsets associated with the 1912 earthquake (Mw 7.4) along the North Anatolian Fault (Gaziköy–Saros segment) allow us to survey (using DGPS) the co‐seismic and cumulative slip distribution. The damage distribution and surface breaks related with the earthquake show an elongated zone of maximum intensity (X MSK) parallel to the fault rupture on land but this may extend offshore to the north‐east and south‐west. Detailed mapping of the fault using topographic maps and aerial photographs indicates the existence of pull‐apart basins and pressure ridges. At several localities, the average 1912 offset along strike is 3.5–4 m and cumulative slip is 2–6 times that of individual movement. The fault rupture geometry and slip distribution suggest the existence of three subsegments with a combined total length of 110–120 km, a fault length and maximum slip similar to those of the 1999 Izmit earthquake. The amount of slip at the north‐easternmost section and in the coastal region of the Sea of Marmara reaches an average 4 m, thereby implying the offshore extension of the 1912 rupture. The results suggest that the 1912 event generated up to 150 km of surface faulting, which would imply a Mw 7.2–7.4 earthquake and which, added with rupture lengths of the 1999 earthquakes, help to constrain the remaining seismic gap in the Sea of Marmara.  相似文献   

19.
Seismic hazard is associated with recent and present fault activity in mountain ranges. In the Betic-Rif alpine mountain chain, tectonic activity started in the Cretaceous, and topographic uplift continues since Tortonian times as a consequence of the NW-SE oblique convergence between Africa and Eurasia. The deformation is active and produces seismicity that sometimes has catastrophic consequences. The Al Hoceima earthquake (February 24, 2004), considered one of the largest earthquakes ever recorded instrumentally in the westernmost Mediterranean (M = 6.3), caused great damage in the region. Seismological studies agree that the main shock was situated on land, at the limit between the External and Internal Zones of the Rif, at a depth of 10-14 km. The focal mechanism points to a strike-slip solution with a NW-SE oriented P axis, quite similar to those of the significant 1994 earthquake swarm located to the north. The epicenter aftershocks distribution would signal the presence of a N-S oriented sinistral fault, activated by the NW-SE regional compression associated to plate boundary convergence. In this setting, the seismogenic fault ruptures related to these seismic events are expected to have reached the Earth's surface. However, detailed field work carried out 1 month after the earthquake does not evidence any N-S strike-slip coseismic fault in the epicentral area. The main observed effects were landslides, damages to constructions, and locally open cracks indicating an unexpected NW-SE extension. Scarce N-S faults are normal, the main ones being located several kilometers away from the epicentral area. To explain this apparent contradiction between geological and seismological observations, we propose a decoupled tectonic model with crustal detachments that separate a deep brittle crust from an upper crust undergoing uplift, and the development of large folds and normal faults. This geological setting, common to internal zones of cordilleras, may need to be taken into account in future paleoseismicity studies and in the assessment of seismic hazard.  相似文献   

20.
福建仙游位于福建省东南沿海中部,其周边地区历史地震活动较平静,属于弱震区。但自从该地区的金钟水库于2010年5月下闸蓄水后,库区附近的地震活动性随之增强。为深入了解该地区的地震活动性、地震分布特征以及寻找隐伏断层,利用中国地震局提供的地震初至震相数据,使用双差定位方法对仙游地区近10年发生的地震进行重定位,获得了更为精确的震源位置,并根据重定位结果模拟深部断裂,寻找隐伏断层。结果显示：(1)重定位后的震源位置更加集中,按照发震时间可分为4个活动区,主要沿沙县—南日岛的次级断裂石苍断裂两侧北西向线性分布。(2)重定位后仙游震群的震源深度主要为8～11 km。石苍断裂左侧地震条带震源深度为6～12 km;右侧地震条带呈现明显的分层现象,上层西北侧地震较为分散,东南侧地震分布较紧凑,震源深度同左侧一样为6～12 km,而下层地震较少,震源深度为14～23 km。(3)根据重定位后的震源位置,利用奇异值分解法拟合得到三个深部断层面,其倾向均为南西向,走向为北西向,与石苍断裂和潼关断裂的倾向和走向一致。结合前人研究成果和本研究结果,推测石苍断裂并不是主发震断层,而是其两侧存在的深部断裂(高倾角隐...  相似文献   

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