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1.
During May 2003 a swarm of 16 earthquakes (ML = 0.6–2.1) occurred at Anjalankoski, south-eastern Finland. The activity lasted for three weeks, but additional two events were observed at the same location in October 2004. A comparison of the waveforms indicated that the source mechanisms and the hypocentres of the events were nearly identical.A relative earthquake location method was applied to better define the geometry of the cluster and to identify the fault plane associated with the earthquakes. The relocated earthquakes aligned along an ENE–WSW trending zone, with a lateral extent of about 1.0 km by 0.8 km. The relative location and the waveform-modelling of depth sensitive surface wave (Rg) and S-to-P converted body wave (sP) phases indicated that the events were unusually shallow, most likely occurring within the first 2 km of the surface. The revised historical earthquake data confirm that shallow swarm-type seismicity is characteristic to the area.The focal mechanism obtained as a composite solution of the five strongest events corresponds to dip-slip motion along a nearly vertical fault plane (strike = 250°, dip = 80°, rake = 90°). The dip and strike of this nodal plane as well as the relocated hypocentres coincide with an internal intrusion boundary of the Vyborg rapakivi batholith.The events occur under a compressive local stress field, which is explained by large gravitational potential energy differences and ridge-push forces. Pore-pressure changes caused by intrusion of ground water and/or radon gas into the fracture zones are suggested to govern the swarm-type earthquake activity.  相似文献   

2.
In the early morning hours on Wednesday November 08, 2006 at 04:32:10(GMT) a small earthquake of ML 4.1 has occurred at southeast Beni-Suef, approximately 160 km SEE of Cairo, northern Egypt. The quake has been felt as far as Cairo and its surroundings while no casualties were reported. The instrumental epicentre is located at 28.57°N and 31.55°E. Seismic moment is 1.76 E14 Nm, corresponding to a moment magnitude Mw 3.5. Following a Brune model, the source radius is 0.3 km with an average dislocation of 1.8 cm and a 2.4 MPa stress drop. The source mechanism from a first motion fault plane solution shows a left-lateral strike-slip mechanism with a minor dip-slip component along fault NNW striking at 161°, dipping 52° to the west and rake −5°. Trend and plunging of the maximum and minimum principle axes P/T are 125°, 28°, 21°, and 23°, respectively. A comparison with the mechanism of the October, 1999 event shows similarities in faulting type and orientation of nodal planes.Eight small earthquakes (3.0  ML < 5.0) were also recorded by the Egyptian National Seismological Network (ENSN) from the same region. We estimate the source parameters and fault mechanism solutions (FMS) for these earthquakes using displacement spectra and P-wave polarities, respectively. The obtained source parameters including seismic moments of 4.9 × 1012–5.04 × 1015 Nm, stress drops of 0.2–4.9 MPa and relative displacement of 0.1–9.1 cm. The azimuths of T-axes determined from FMS are oriented in NNE–SSW direction. This direction is consistent with the present-day stress field in Egypt and the last phase of stress field changes in the Late Pleistocene, as well as with recent GPS measurements.  相似文献   

3.
N. Kraeva   《Tectonophysics》2004,383(1-2):29-44
Application of Tikhonov's technique, using input errors for the parameter of regularization estimation, enhances the accuracy and stability of the reconstruction of a source time function (STF) by the empirical Green function (EGF) method that gives us an opportunity to use simultaneously for analysis body and surface waves data, and to estimate the horizontal and vertical directivity effects. Knowledge of the last is particularly useful for the choice of an active nodal plane of earthquakes with the dip slip fault orientation that allows us to classify these earthquakes to the interplate or intraplate types and thereby to reach the better understanding of tectonic processes in the region of interest.By way of illustration, an attempt to estimate average parameters of faulting in a first approximation is made herein for two Russian Far East large events with opposite types of focal mechanism orientation, strike slip and dip slip. The former is not a matter of interest in the context of vertical directivity effect but enables us to test the method.The directivity analysis of pulse durations and inverse amplitudes of the relative source time functions (RSTFs) restored at eight globally distributed stations IRIS indicates that the destruction in the source of the Neftegorsk earthquake (05/27/1995 MW=7.1) propagated roughly horizontally in the direction 8±11° during 19.2±0.4 s along the rupture extending 35.5±4.9 km. The calculated slip distribution along the rupture coincides within the error with the results of field geological measurements on the causal surface fault that proves that the Neftegorsk earthquake source is well described by the model of the linear unilateral fault and gives a good assessment of the method applied.The average parameters of faulting in the Kamchatka earthquake (03/08/1999 MW=6.9) have been determined from data of 13 station IRIS. It was shown that the destruction in its source propagated downward at an angle of about 60° with horizon, in the direction about S156° E, during 13.4±0.2 s, along the rupture totaling 25.5±2.3 km in length. Therefore, the nodal plane, steeply dipped to the SE, was active and this event can be regarded as an intraplate type. Two asperities can be selected; the first with the maximum slip 3.3 m located at a distance of about 7 km from the onset of rupture, and the second with the maximum slip about 0.9 m centered at approximately 19 km from that.  相似文献   

4.
Results from a recent earthquake in the Eastern Pyrenees are presented and the seismotectonics of the region is analyzed from the presently available data. On 26 September 1984 an earthquake (ML = 4.4) took place in the area of the historical destructive earthquake of 1428. Several portable stations installed in the epicentral area to record aftershocks permitted of defining a precise location at 42°19.2′N, 2°10.2′E and 5 km depth. A maximum felt intensity of V (MSK) is obtained from macroseismic data. The epicentral location lies within a block bounded by E-W-trending structures and the focal solution shows right-lateral shearing with a NW-SE pressure axis.The seismicity in the Eastern Pyrenees shows a complex pattern which can be associated with both E-W fractures and NE-SW fault systems. Focal solutions of another two recent earthquakes of ML ~ 4, with differences in horizontal pressure axis, are also discussed.  相似文献   

5.
F. Di Luccio  E. Fukuyama  N.A. Pino   《Tectonophysics》2005,405(1-4):141-154
On October 31, 2002 a ML = 5.4 earthquake occurred in southern Italy, at the margin between the Apenninic thrust belt (to the west) and the Adriatic plate (to the east). In this area, neither historical event nor seismogenic fault is reported in the literature. In spite of its moderate magnitude, the earthquake caused severe damage in cities close to the epicenter and 27 people, out of a total of 29 casualties, were killed by the collapse of a primary school in S. Giuliano di Puglia. By inverting broadband regional waveforms, we computed moment tensor solutions for 15 events, as small as ML = 3.5 (Mw = 3.7). The obtained focal mechanisms show pure strike-slip geometry, mainly with focal planes oriented to NS (sinistral) and EW (dextral). In several solutions focal planes are rotated counterclockwise, in particular for later events, occurring west of the mainshock. From the relocated aftershock distribution, we found that the mainshock ruptured along an EW plane, and the fault mechanisms of some aftershocks were not consistent with the mainshock fault plane. The observed stress field, resulting from the stress tensor inversion, shows a maximum principal stress axis with an east–west trend (N83°W), whereas the minimum stress direction is almost N–S. Considering both the aftershock distribution and moment tensor solutions, it appears that several pre-existing faults were activated rather than a single planar fault associated with the mainshock. The finite fault analysis shows a very simple slip distribution with a slow rupture velocity of 1.1 km/s, that could explain the occurrence of a second mainshock about 30 h after. Finally, we attempt to interpret how the Molise sequence is related to the normal faulting system to the west (along the Apennines) and the dextral strike-slip Mattinata fault to the east.  相似文献   

6.
A data set of three-component short-period digital seismograms recorded in Friuli after the strong earthquake of 6th May 1976, allowed the local magnitude ML and the seismic moment M0 to be estimated in the range 0 < ML < 2. The data set including the same parameters for the higher-magnitude Friuli events (ML 5) shows two different slopes for the relation Log M0 = CML + d for the two different ranges of ML. One finds C ~ 1.0 (for 0 < ML < 2) and C ~1.5 (for5 ML 6.2), respectively.This implies that apparent stress release increases at low magnitudes, while it appears to be comparatively independent of the magnitude and to have an average value of about 100 bar for higher-magnitude earthquakes. Conversely, the fault dimensions do not appear to be magnitude-dependent for ML < 2; for higher-magnitude events the linear fault dimensions range from about 1 km at ML ~ 5 to about 12 km for the strong earthquake of 6th May 1976 (ML = 6.2).  相似文献   

7.
The 26 November 2005 Jiujiang-Ruichang, Jiangxi, Ms?5.7 earthquake occurred in a seismotectonic setting of moderate earthquake. The northwest-trending Xiangfan-Guangji fault (XFG) does not enter into the epicenter vicinity, but the northeast-trending Ruichang-Wuning fault (RWF) as a regional fault extends to the epicenter nearby, appearing as the Ruichang basin and its marginal faults. Tilting of the Ruichang Basin (RCB) in the Quaternary was controlled by the RCB southeast-marginal, buried fault (RSMBF). Shallow geophysical survey reveals that the RSMBF caused an offset of the reflection layers. Drill hole columnar section demonstrates that there are about 10–12?m displacement in the lower section of the middle-Pleistocene Series along the RSMBF, but no disruption is found in the upper section of the middle-Pleistocene Series. The RSMBF not only has activity in the Quaternary, but also coincides with the nodal plane I from the focal mechanism of the Jiujiang-Ruichang Ms?5.7 earthquake. This evidence, including aftershock distribution and isoseismic lines, strongly suggests that the RSMBF might be the seismogenic tectonics. The RWF is discontinuous at the surface, and consists of three en echelon Quaternary basins, which are the Ruichang, Fanzhen and Wuning basins. Three moderate earthquakes, the Fanzhen ML?4.9 earthquake, the Yejiapu ML?4.1 earthquake and the Jiujiang-Ruichang Ms?5.7 earthquake, have happened in the basins since 1995. The seismogenic tectonics of the Jiujiang-Ruichang Ms?5.7 earthquake is not isolated, but may be controlled by the RWF at depth, the slip of which causes the accumulation of energy for earthquake occurrence.  相似文献   

8.
A 10-station portable seismograph network was deployed in northern Greece to study aftershocks of the magnitude (mb) 6.4 earthquake of June 20, 1978. The main shock occurred (in a graben) about 25 km northeast of the city of Thessaloniki and caused an east-west zone of surface rupturing 14 km long that splayed to 7 km wide at the west end. The hypocenters for 116 aftershocks in the magnitude range from 2.5 to 4.5 were determined. The epicenters for these events cover an area 30 km (east-west) by 18 km (north-south), and focal depths ranges from 4 to 12 km. Most of the aftershocks in the east half of the aftershock zone are north of the surface rupture and north of the graben. Those in the west half are located within the boundaries of the graben. Composite focalmechanism solutions for selected aftershocks indicate reactivation of geologically mapped normal faults in the area. Also, strike-slip and dip-slip faults that splay off the western end of the zone of surface ruptures may have been activated.The epicenters for four large (M 4.8) foreshocks and the main shock were relocated using the method of joint epicenter determination. Collectively, those five epicenters form an arcuate pattern convex southward, that is north of and 5 km distant from the surface rupturing. The 5-km separation, along with a focal depth of 8 km (average aftershock depth) or 16 km (NEIS main-shock depth), implies that the fault plane dips northward 58° or 73°, respectively. A preferred nodal-plane dip of 36° was determined by B.C. Papazachos and his colleagues in 1979 from a focal-mechanism solution for the main shock. If this dip is valid for the causal fault and that fault projects to the zone of surface rupturing, a decrease of dip with depth is required.  相似文献   

9.
We determine the source parameters of three minor earthquakes in the Upper Rhine Graben (URG), a Cenozoic rift, using waveforms from permanent and temporary seismological stations. Two shallow thrust-faulting events (M L = 2.4 and 1.5) occurred on the rift shoulder just south of Heidelberg in March 2005. They indicate a possible movement along the sediment–crystalline interface due to tectonic loading from the near-by Odenwald. In February 2005, an earthquake with a normal-faulting mechanism occurred north of Speyer. This event (M L = 2.8) had an unusual depth of about 22 km and a similar deep normal-faulting event occurred there in 1972 (M L = 3.2). Other lower crustal events without fault plane solutions are known from 1981 and 1983. At such a depth, inside the lower crust, ductile behaviour instead of brittle faulting is commonly assumed and used for geodynamic modelling. Based on the newly available fault plane solutions we can confirm the brittle, extensional regime in the upper and lower crust in the central to northern URG indicated in earlier studies.  相似文献   

10.
On February 13, 1981 a relatively strong earthquake occurred in the Lake Vänern region in south-central Sweden. The shock had a magnitude ofML = 3.3 and was followed within three weeks by three aftershocks, with magnitudes 0.5 ≤ ML ≤ 1.0. The focal mechanism solution of the main shock indicates reverse faulting with a strike in the N-S or NE-SW direction and a nearly horizontal compressional stress. The aftershocks were too small to yield data for a full mechanism solution, but first motions of P-waves, recorded at two stations, are consistent for the aftershocks. Dynamic source parameters, derived from Pg- and Sg-wave spectra, show similar stress drops for the main shock (2 bar) and the aftershocks (1 bar), while the differences in seismic moment (1.5·1020 resp. 4·1018dyne cm), fault length (0.7 resp. 0.2 km) and relative displacement (0.15 resp. 0.03 cm) are significant.  相似文献   

11.
A large earthquake of magnitude MW = 6.3 occurred on 14 August 2003 NW of the Lefkada Island, which is situated at the Ionian Sea (western Greece). The source parameters of this event are determined using body-wave modeling. The focal depth was found equal to 9 km, the constrained focal mechanism revealed dextral strike–slip motion (φ = 15°, Δ = 80° and λ = 170°), the duration of the source time function was 8 s and the seismic moment 2.9 × 1025 dyn cm. The earthquake occurred close to the northern end of the Kefallinia transform fault, where the 1994 moderate event and its aftershock sequence were also located. The epicentral distribution of the 2003 aftershock sequence revealed the existence of two clusters. The first one is located close to the epicentral area of the mainshock, while the second southern, close to the northwestern coast of the Kefallinia Island. A gap of seismicity is observed between the two clusters. The length of the activated zone is approximately 60 km. The analysis of data revealed that the northern cluster is directly related to the mainshock, while the southern one was triggered by stress transfer caused by the main event.  相似文献   

12.
The 14 November 2001 Kunlun, China, earthquake with a moment magnitude (Mw) 7.8 occurred along the Kusai Lake–Kunlun Pass fault of the Kunlun fault system. We document the spatial distribution and geometry of surface rupture zone produced by this earthquake, based on high-resolution satellite (Landsat ETM, ASTER, SPOT and IKONOS) images combined with field measurements. Our results show that the surface rupture zone can be divided into five segments according to the geometry of surface rupture, including the Sun Lake, Buka Daban–Hongshui River, Kusai Lake, Hubei Peak and Kunlun Pass segments from west to east. These segments, each 55 to 130 km long, are separated by step-overs. The Sun Lake segment extends about 65 km with a strike of N45° 75°W (between 90°05′E 90°50′E) along the previously unrecognized West Sun Lake fault. A gap of about 30 km long exists between the Sun Lake and Buka Daban Peak where no obvious surface ruptures can be observed either from the satellite images or field observations. The Buka Daban–Hongshui River, Kusai Lake, Hubei Peak and Kunlun Pass segments run about 365 km striking N75° 85°W along the southern slope of the Kunlun Mountains (between 91°07′E 94°58′E). This segmentation of the surface rupture is well correlated with the pattern of slip distribution measured in the field. Detailed mapping suggest that these five first-order segments can be further separated into over 20 second-order segments with a length of 10–30 km, linked by smaller scale step-overs or bends.Our result also shows that the total coseismic surface rupture length produced by the 2001 Kunlun earthquake is about 430 km (excluding the 30-km-long gap), which is the longest coseismic surface rupture for an intracontinental earthquake ever recorded.Finally, we suggest a multiple bilateral rupture propagation model that shows the rupture process of the 2001 Mw 7.8 earthquake is complex. It consists of westward and eastward rupture propagations and interaction of these bilateral rupture processes.  相似文献   

13.
The Killari earthquake of September 29, 1993 (Mw=6.2) in peninsular India triggered several aftershocks that were recorded by a network of 21 stations. We computed the change in regional static stress caused by coseismic slip on the earthquake rupture and correlated it with the aftershocks with a view to constrain some of the rupture parameters of this earthquake. We evaluated the six available estimates of fault plane solutions for this earthquake and concluded that reverse slip on a 42° dipping, N112° trending fault, which extends up to the surface from a depth of 7 km, produces maximum correlation between the increased static stress and aftershock distribution. Our analysis suggests that the majority of coseismic slip occurred on the part of the rupture that lies in the depth range of 3–6.5 km.  相似文献   

14.
2003年青海德令哈地震序列的重新定位和发震构造   总被引：4，自引：0，他引：4  
应用交切法对2003年4月17日德令哈地震序列的ML=6.7主震和截止至2003年10月25日的ML小于1.0级的余震,共117次地震事件进行了初始定位,并以双差地震定位法对这些地震重新进行精确定位。认为德令哈地震序列的主震震中位置为37.566°N,96.509°E,震源深度为13km,余震震源空间位置分布与哈佛大学震源机制解给出的走向为294°的节面一致。德令哈地震序列重新精确定位的结果清楚地表明了穿过震区的走向NWW—SEE、倾向NE的大柴旦—宗务隆山现代活动断裂带是这次德令哈地震序列的发震构造,同时表明该区域应力场水平最大主应力方向范围大致在N24°E—N34°E。  相似文献   

15.
Katsuyuki Abe   《Tectonophysics》1975,27(3):223-238
The source mechanism of the Saitama earthquake (36.07°N,139.40°E, Ms = 5.4) of July 1, 1968, is studied on the basis of P-wave first motion, aftershock, long-period surface-wave data and low-magnification long-period seismograms recorded in the nearfield. A precise location of the aftershocks is made using P and S—P time data obtained by a micro-earthquake observatory network. The synthetic near-field seismograms based on the Haskell model are directly compared with the observed near-field seismograms for wave form and amplitude to determine the dynamic fault parameters. The results obtained are as follows: source geometry, reverse dip slip with considerable right-lateral strike-slip component; dip direction, N6°E; dip angle 30°; fault dimension, 10 × 6 km2; rupture velocity, 3.4 km/sec in the direction S30°E; average dislocation, 92 cm; average dislocation velocity, 92 cm/sec; seismic moment, 1.9 · 1025 dyn-cm; stress drop, 100 bar. The effective stress is about the same as the stress drop. For major earthquakes in the Japanese Islands, the dislocation velocity, .D, is found to be proportional to the stress drop, σ. This relation can be expressed by .D - (β/μ)σ, where β is the shear velocity and μ is the rigidity. This result has an importance in engineering seismology because the stress drop scales the seismic motion in the vicinity of an earthquake fault.  相似文献   

16.
An Mb = 5.1 earthquake occurred on February, 29, 1980, in the Western Pyrenees near Arudy (France). The telemetred network of the I.P.G.P., operating in this area since 1978, allowed a good localization of this earthquake (43°4.21′N, 0°24.59′W, depth 4km). During the two years preceding this earthquake the seismic activity exhibited a gradual decrease. A foreshock of magnitude 1.6 was recorded three hours before the main shock.A temporary network set up in the epicentral area a few days after the main shock permitted a precise study of the aftershock sequence. Fifty fault-plane solutions for earthquakes ranging from magnitude 1.5-4 were obtained. A complex pattern of faulting was revealed, with both strike-slip and normal faulting. However, a regional tectonic stress tensor can be proposed from a detailed investigation of the aftershock sequence. This stress tensor is in agreement with previous results in this area.  相似文献   

17.
Papadimitriou  P.  Voulgaris  N.  Kassaras  I.  Kaviris  G.  Delibasis  N.  Makropoulos  K. 《Natural Hazards》2002,27(1-2):15-33
On 7 September 1999 at 11:56 GMT a destructive earthquake (Mw = 6.0) occurred close to Athens (Greece). The rupture process is examined using data from the Cornet local permanent network, as well as teleseismic recordings. Data recorded by a temporary seismological network were analyzed to study the aftershock sequence. The mainshock was relocated at 38.105°N, 23.565°E, about 20 km northwest of Athens. Four foreshocks were also relocated close to the mainshock. The modeling of teleseismic P and SH waves provides a well-constrained focal mechanism of the mainshock (strike = 105°, dip = 55° and rake = -80°) at a depth of 8 km and a seismic moment M0 = 1.01025 dyn·cm. The obtained fault plane solution represents normal faulting indicating an almost north-south extension. More than 3500 aftershocks were located, 1813 of which present RMS < 0.1 s and ERH, ERZ < 1.0 km. Two main clusters were distinguished, while the depth distribution is concentrated between 2 and 11 km. Over 1000 fault plane solutions of aftershocks were constrained, the majority of which also correspond to N–S extension. No surface breaks were observed but the fault plane solution of the mainshock is in agreement with the tectonics of the area and with the focal mechanisms obtained by aftershocks. The hypocenter of the mainshock is located on the deep western edge of the fault plane. The relocated epicenter coincides with the fringe that represents the highest deformation observed on the differential interferometric image. The calculated source duration is 5 sec, while the estimated dimensions of the fault are 15 km length and 10 km width. The source process is characterized by unilateral eastward rupture propagation, towards the city of Athens. An evident stop phase observed in the recordings of the Cornet local stations is interpreted as a barrier caused by the Aegaleo Mountain.  相似文献   

18.
We revisit the April 1979 Montenegro earthquake sequence to invert for finite-fault slip models for the mainshock of 15 April 1979 (Mw 7.1) and of the strongest aftershock of 24 May 1979 (Mw 6.2) using P, SH and SV waveforms, retrieved from IRIS data center. We also used body waveform modelling inversion to confirm the focal mechanism of the mainshock as a pure thrust mechanism and rule out the existence of considerable strike slip component in the motion. The mainshock occurred along a shallow (depth 7 km), low angle (14°) thrust fault, parallel to the coastline and dipping to the NE. Our preferred slip distribution model for the mainshock indicates that rupture initiated from SE and propagated towards NW, with a speed of 2.0 km/s. Moment was released in a main slip patch, confined in an area of L  50 km × W  23 km. The maximum slip ( 2.7 m) occurred  30 km to the NW of the hypocenter (location of rupture initiation). The average slip is 49 cm and the total moment release over the fault is 4.38e19 Nm. The slip model adequately fits the distribution of the Mw ≥ 4.3 aftershocks, as most of them are located in the regions of the fault plane that did not slip during the mainshock. The 24 May 1979 (Mw 6.2) strongest aftershock occurred  40 km NW of the mainshock. Our preferred slip model for this event showed a characteristic two-lobe pattern, where each lobe is  7.5 × 7.5 km2. Rupture initiated in the NW lobe, where the slip obtained its maximum value of 45 cm, very close to the hypocenter, and propagated towards the south-eastern lobe where it reached another maximum value — for this lobe — of 30 cm, approximately 10 km away from the hypocenter. To indirectly validate our slip models we produced synthetic PGV maps (Shake maps) and we compared our predictions with observations of ground shaking from strong motion records. All comparisons were made for rock soil conditions and in general our slip models adequately fit the observations especially at the closest stations where the shaking was considerably stronger. Through the search of the parameter space for our inversions we obtained an optimum location for the mainshock at 42.04°N and 19.21° E and we also observed that better fit to the observations was obtained when the fault was modeled as a blind thrust fault.  相似文献   

19.
In the present work a detailed seismotectonic study of the broader area of the Mygdonia basin (N. Greece) is performed. Digital data for earthquakes which occurred in the broader Mygdonia basin and were recorded by the permanent telemetric network of the Geophysical Laboratory of the Aristotle University of Thessaloniki during the period 1989–1999 were collected and fault plane solutions for 50 earthquakes which occurred in the study area were calculated with a modified first motions approach which incorporates amplitude and radiation pattern information. Fault plane solutions for the 3 main shocks of Volvi (23/05/78, MW = 5.8 and 20/06/78, MW = 6.5) and Arnaia (04/05/95, MW = 5.8) events and the 1978 aftershock sequence were additionally used. Moreover, data from two local networks established in the Mygdonia basin were also incorporated in the final dataset.Determination of the stress field was realized by the use of the method of Gephart and Forsyth [Gephart, J.W., Forsyth, D.W., 1984. An improved method for determining the regional stress tensor using earthquake focal mechanism data: application to the San Fernando earthquake sequence: Jour. Geophys. Res., v.89, no. B11, p. 9305–9320] for the stress tensor inversion and the results were compared with independent estimates based on the calculation of the average moment tensor [Papazachos, C.B.,Kiratzi, A.A., 1992. A formulation for reliable estimation of active crustal deformation and its application to central Greece. Geophys. J. Int. 111, 424–432]. The obtained stress results show a relatively good agreement between the two approaches, with differences in the azimuth of the dominant extension axis of the order of 10°. Furthermore, comparison with independent information for the mean stress axes provided by the study of kinematics on neotectonic faults [Mountrakis, D., Kilias, A., Tranos, M., Thomaidou, E., Papazachos, C., Karakaisis, G., Scordilis, E., Chatzidimitriou, P., Papadimitriou, E., Vargemezis, G., Aidona, E., Karagianni, E., Vamvakaris, D. Skarlatoudis, A. 2003. Determination of the settings and the seismotectonic behavior of the main seismic-active faults of Northern Greece area using neotectonic and seismological data. Earthquake Planning and Protection Organisation (OASP) (in Greek)] shows a similar agreement with typical misfit of the order 10°. The stress inversion method was modified in order to select one or both nodal planes of the focal mechanism which corresponds to the “true” fault plane of the occurred earthquakes and was able to select a single fault plane in the majority of examined cases. Using this approach, the obtained fault plane rose diagrams are in agreement with results from various neotectonic studies. Moreover, several secondary active fault branches were identified, which are still not clearly observed in the field.  相似文献   

20.
This paper presents the computation of time series of the 22 July 2007 M 4.9 Kharsali earthquake. It occurred close to the Main Central Thrust (MCT) where seismic gap exists. The main shock and 17 aftershocks were located by closely spaced eleven seismograph stations in a network that involved VSAT based real-time seismic monitoring. The largest aftershock of M 3.5 and other aftershocks occurred within a small volume of 4 × 4 km horizontal extent and between depths of 10 and 14 km. The values of seismic moment (M ∘) determined using P-wave spectra and Brune’s model based on f 2 spectral shape ranges from 1018 to 1023 dyne-cm. The initial aftershocks occurred at greater depth compared to the later aftershocks. The time series of ground motion have been computed for recording sites using geometric ray theory and Green’s function approach. The method for computing time series consists in integrating the far-field contributions of Green’s function for a number of distributed point source. The generated waveforms have been compared with the observed ones. It has been inferred that the Kharsali earthquake occurred due to a northerly dipping low angle thrust fault at a depth of 14 km taking strike N279°E, dip 14° and rake 117°. There are two regions on the fault surface which have larger slip amplitudes (asperities) and the rupture which has been considered as circular in nature initiated from the asperity at a greater depth shifting gradually upwards. The two asperities cover only 10% of the total area of the causative fault plane. However, detailed seismic imaging of these two asperities can be corroborated with structural heterogeneities associated with causative fault to understand how seismogenesis is influenced by strong or weak structural barriers in the region.  相似文献   

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