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1.
Abstract: Four months after the Wenchuan Ms 8 earthquake in western Sichuan, China, in situ stress measurements were carried out along the Longmenshan fault zone with the purpose of obtaining stress parameters for earthquake hazard assessment. In-situ stresses were measured in three new boreholes by using overcoring with the piezomagnetic stress gauges for shallow depths and hydraulic fracturing for lower depths. The maximum horizontal stress in shallow depths (~20 m) is about 4.3 MPa, oriented N19°E, in the epicenter area at Yingxiu Town, about 9.7 MPa, oriented N51°W, at Baoxing County in the southwestern Longmenshan range, and about 2.6 MPa, oriented N39°E, near Kangding in the southernmost zone of the Longmenshan range. Hydraulic fracturing at borehole depths from 100 to 400 m shows a tendency towards increasing stress with depth. A comparison with the results measured before the Wenchuan earthquake along the Longmenshan zone and in the Tibetan Plateau demonstrates that the stress level remains relatively high in the southwestern segment of the Longmenshan range, and is still moderate in the epicenter zone. These results provide a key appraisal for future assessment of earthquake hazards of the Longmenshan fault zone and the aftershock occurrences of the Wenchuan earthquake.  相似文献   

2.
Four months after the Wenchuan Ms 8 earthquake in western Sichuan, China, in situ stress measurements were carried out along the Longmenshan fault zone with the purpose of obtaining stress parameters for earthquake hazard assessment. In-situ stresses were measured in three new boreholes by using overcoring with the piezomagnetic stress gauges for shallow depths and hydraulic fracturing for lower depths. The maximum horizontal stress in shallow depths (～20 m) is about 4.3 MPa, oriented NI9°E, in the epicenter area at Yingxiu Town, about 9.7 MPa, oriented N51°W, at Baoxing County in the southwestern Longmenshan range, and about 2.6 MPa, oriented N39°E, near Kangding in the southernmost zone of the Longmenshan range. Hydraulic fracturing at borehole depths from 100 to 400 m shows a tendency towards increasing stress with depth. A comparison with the results measured before the Wenchuan earthquake along the Longmenshan zone and in the Tibetan Plateau demonstrates that the stress level remains relatively high in the southwestern segment of the Longmenshan range, and is still moderate in the epicenter zone. These results provide a key appraisal for future assessment of earthquake hazards of the Longmenshan fault zone and the aftershock occurrences of the Wenchuan earthquake.  相似文献   

3.
汶川地震后沿龙门山裂断带原地应力测量初步结果   总被引：2，自引：0，他引：2  
2008年5月12日在中国四川省西部汶川发生Ms8.0地震,震中位于青藏东缘龙门山断裂带。地震发生后的4个月,沿龙门山断裂带中南段开展了原地应力测量,获得了3个测点的应力大小和方向。在3个测孔中浅部采用压磁应力解除法,深部采用水压致裂法。浅部测量结果显示,位于震中区映秀测点,水平最大主应力值为4.3MPa,最大主应力方向为N19°E;宝兴测点位于震中区西南的龙门山断裂带南段,汶川地震没有导致该段地表破裂,该点获得的水平最大主应力值为9.8MPa,最大主应力方向为N51°W;位于龙门山断裂带最西南端的康定测点,水平最大主应力值为2.6MPa,最大主应力方向为N39°E。利用水压致裂法对各钻孔100～400m深度进行了应力测量,获得了应力随深度变化趋势和应力状态。与震前其它应力测量结果和中国其它地区表层地应力测量结果比较,龙门山断裂带西南段处于相对高应力水平,震中区仍处于中等应力水平。这项研究成果将为评价龙门山断裂带余震和今后强震发展趋势提供关键构造物理参数。  相似文献   

4.
A comparison of three methods of stress determination using overcoring tests, earthquake focal-mechanism solutions, and fault-displacement analysis, was carried out near the epicentres of the 1968 Meckering and the 1970 Calingiri earthquakes, Western Australia. Shallow overcoring measurements (3–10 m) were made at seven sites in competent granite, along a 200-km north—south traverse through the location of the Meckering earthquake. The in situ measurements indicate a high regional compressive stress, acting about N77°E. This compares with the direction of the P-axes from the Meckering and Calingiri earthquakes of N91°E and N102°E, respectively, and east-west orientation of major principal stress deduced from observations of surface faulting. The highest maximum principal stress, 23 MPa, was measured at the site farthest north from the Meckering epicentre (~ 90 km), and the lowest, 4 MPa, was measured near the epicentre. The magnitude of the stress increases with distance away from the epicentral area at about 0.2 kPa/m. The results were corrected for drilling water temperature, thermal rock stresses, and suction pore pressure. The total correction was less than 2 MPa at most sites.Estimates of shear stress release from the fault-scarp displacements for Meckering and Calingiri were of similar magnitude (~10 MPa) to the difference between observed shear stress at sites close to and sites remote from the Meckering earthquake.As a cause of the earthquake it is proposed that the fault plane is progressively weakened by alteration or weathering, and that a small long-term fluctuation of head of ground water was the trigger.The high stress at shallow depths, the growing evidence of east—west major principal stress in most of the Australian continent, and the existence of horizontal stress higher than gravity lithostatic stress may have a common explanation, in terms of the driving forces of plate tectonics. The Australian results do not agree with the north—south orientation suggested by crude plate-drift theories in which the major stress is in the direction of the drift, and do not appear to fit with orientations from other continents, in the Richardson et al. (1976) interacting plate model which assumes a velocity-dependent plate driving force. An analysis of driving forces at diverging plate boundaries was carried out and suggests no dominant force-velocity relationship, thus forces independent of plate velocity may control the stress orientation in the plate.  相似文献   

5.
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   

6.
In the southern South–North Seismic Zone, China, seismic activity in the Yingjiang area of western Yunnan increased from December 2010, and eventually a destructive earthquake of Ms5.9 occurred near Yingjiang town on 10 March 2011. The focal mechanism and hypocenter location of the mainshock suggest that the Dayingjiang Fault was the site of the mainshock rupture. However, most of foreshocks and all aftershocks recorded by a portable seismic array located close to the mainshock occurred along the N–S-striking Sudian Fault, indicating that this fault had an important influence on these shocks. Coulomb stress calculations show that three strong(magnitude ≥5.0) earthquakes that occurred in the study region in 2008 increased the coulomb stress along the plane parallel to the Dayingjiang Fault. This supports the Dayingjiang Fault, and not the Sudian Fault, as the seismogenic fault of the 2011 Ms5.9 Yingjiang earthquake. The strong earthquakes in 2008 also increased the Coulomb stress at depths of ≤5 km along the entire Sudian Fault, and by doing so increased the shallow seismic activity along the fault. This explains why the foreshocks and aftershocks of the 2011 Yingjiang earthquake were located mostly on the Sudian Fault where it cuts the shallow crust. The earthquakes at the intersection of the Sudian and Dayingjiang faults are distributed mainly along a belt that dips to the southeast at ~40°, suggesting that the Dayingjiang Fault in the mainshock area also dips to the southeast at ~40°.  相似文献   

7.
Although the Southwest Seismic Zone (SWSZ), located about 150 km to the east of Perth in southwestern Australia, is one of the most seismically active areas in Australia, there is little understanding as to why the earthquakes are occurring.An analysis of geophysical, geological and geodetic data from the area suggests that the SWSZ coincides with a Precambrian terrane boundary. Seismic data show that the terrane boundary zone dips at a shallow angle in a northeasterly direction. Reactivation of this ‘zone of weakness’ in the contemporary stress field (east–west maximum horizontal stress) is interpreted to be the first-order control on seismicity in the region.Gravity data show that the terrane boundary is offset by near-orthogonal structures, which are interpreted as faults. At least one of these trends corresponds with a linear zone of epicentres. The temporal and spatial distributions of epicentres associated with the 1968 Meckering earthquake (ML 6.9) suggest that the second-order distribution of seismicity in the SWSZ can be explained by the ‘intersection model’, whereby stresses are amplified by space problems associated with displacements on crosscutting faults.It is speculated that a zone of high density and high seismic velocity in the lower crust may also be a second-order control on the local seismicity. However, confirmation awaits better delineation of the extent of this zone.  相似文献   

8.
Seismic imaging together with global positioning system (GPS) and crustal stress data analyses show that the Mw7.9 2008 Wenchuan earthquake occurred within a distinct area of high crustal stress (～ 17.5 MPa) and high Poisson's ratio (7–10%) anomalies centered on the Longmen-Shan (Shan means Mountain in Chinese) tectonic fault belt. Low P-wave and S-wave velocities in the southwest (SW) segment contrast with high-velocity anomalies in the central portion (CP) and northeast (NE) segment within the uppermost ～ 15 km depths along the tectonic fault belt, though a presumably ductile zone with low-velocity anomalies separates the CP and NE segment. The rupture initiated near the southwestern end of the CP at a zone of high Poisson's ratio (σ) which extends down into the lower crust. These low-velocity and high-σ anomalies immediately below the source hypocenter, together with the high crustal stress, indicate the presence of high-pressure fluids from the lower crust, which might have reduced the mechanical strength of the fractured rock matrix and triggered the earthquake. Our study suggests that the structural heterogeneity and high crustal stress played an important role in the nucleation of the Wenchuan earthquake and its rupture process.  相似文献   

9.
Abstract: A three-dimensional local-scale P-velocity model down to 25 km depth around the main shock epicenter region was constructed using 83821 event-to-receiver seismic rays from 5856 aftershocks recorded by a newly deployed temporary seismic network. Checkerboard tests show that our tomographic model has lateral and vertical resolution of ~2 km. The high-resolution P-velocity model revealed interesting structures in the seismogenic layer: (1) The Guanxian-Anxian fault, Yingxiu-Beichuan fault and Wenchuan-Maoxian fault of the Longmen Shan fault zone are well delineated by sharp upper crustal velocity changes; (2) The Pengguan massif has generally higher velocity than its surrounding areas, and may extend down to at least ~10 km from the surface; (3) A sharp lateral velocity variation beneath the Wenchuan-Maoxian fault may indicate that the Pengguan massif’s western boundary and/or the Wenchuan-Maoxian fault is vertical, and the hypocenter of the Wenchuan earthquake possibly located at the conjunction point of the NW dipping Yingxiu-Beichuan and Guanxian-Anxian faults, and vertical Wenchuan-Maoxian fault; (4) Vicinity along the Yingxiu-Beichuan fault is characterized by very low velocity and low seismicity at shallow depths, possibly due to high content of porosity and fractures; (5) Two blocks of low-velocity anomaly are respectively imaged in the hanging wall and foot wall of the Guanxian-Anxian fault with a ~7 km offset with ~5 km vertical component.  相似文献   

10.
In situ stress measurements by hydraulic fracturing were carried out in the 617 m deep borehole specially drilled in the epicentral zone of the 1993 Latur earthquake for the purpose of research. The stress measurements carried out at 592 m depth in this borehole are the deepest of all such measurements made so far in the Indian shield. The maximum and minimum principal horizontal stresses (S H max andS h min) have been derived from the hydrofracture data using the classical method. TheS H max andS h min are found to be 16.5 and 9.6 MPa at 373 m depth, and 25.0 and 14.1 MPa at 592 m depth, indicating that the vertical gradients ofS hmax andS hmin in the epicentral zone are 39 MPa/km and 21 MPa/km respectively. The principal horizontal stresses in the epicentral zone are comparable with those at Hyderabad and 30% higher than in most other comparable intra-continental regions. Analysis of the results indicate that the stresses in the focal region of the 1993 Latur earthquake have not undergone any significant change following its occurrence and this is in agreement with a similar inference drawn from the seismic data analysis. It appears that the Latur earthquake was caused due to rupturing of the overpressured fault segment at the base of the seismogenic zone.  相似文献   

11.
郯庐断裂带山东段深孔地应力测量及其现今活动性分析   总被引：1，自引：0，他引：1  
已有的地表调查和GPS位移测量、深部震源机制等研究结果表明,郯庐断裂山东段现今活动性表现为顺时针压扭性活动特征。为揭示郯庐（郯城－庐江）断裂带山东段地表和深部之间地壳浅表层日本大地震发生后的现今地应力状态和活动特征,在鲁东北部花岗岩地区开展了600 m的钻探工程与地应力测量工作。钻探岩芯编录初步揭示地壳浅表层岩体结构特征,随深度系统的地应力测量结果表明,现今水平主应力起主导作用,易于断层走滑作用发生,且现今最大水平主应力方向为近东西向,反映出郯庐断裂带山东段现今活动特征为压性兼右旋走滑,与地表和深部已有研究成果相吻合。研究成果为郯庐断裂带山东段现今活动性研究补充了新的资料。  相似文献   

12.
The Mw 9.0 Tohoku-Oki earthquake that occurred off the Pacific coast of Japan on March 11, 2011, was followed by thousands of aftershocks, both near the plate interface and in the crust of inland eastern Japan. In this paper, we report on two large, shallow crustal earthquakes that occurred near the Ibaraki-Fukushima prefecture border, where the background seismicity was low prior to the 2011 Tohoku-Oki earthquake. Using densely spaced geodetic observations (GPS and InSAR datasets), we found that two large aftershocks in the Iwaki and Kita-Ibarake regions (hereafter referred to as the Iwaki earthquake and the Kita-Ibarake earthquake) produced 2.1 m and 0.44 m of motion in the line-of-sight (LOS), respectively. The azimuth-offset method was used to obtain the preliminary location of the fault traces. The InSAR-based maximum offset and trace of the faults that produced the Iwaki earthquake are consistent with field observations. The fault location and geometry of these two earthquakes are constrained by a rectangular dislocation model in a multilayered elastic half-space, which indicates that the maximum slips for the two earthquakes are 3.28 m and 0.98 m, respectively. The Coulomb stress changes were calculated for the faults following the 2011 Mw 9.0 Tohoku-Oki earthquake based on the modeled slip along the fault planes. The resulting Coulomb stress changes indicate that the stresses on the faults increased by up to 1.1 MPa and 0.7 MPa in the Iwaki and Kita-Ibarake regions, respectively, suggesting that the Tohoku-Oki earthquake triggered the two aftershocks, supporting the results of seismic tomography.  相似文献   

13.
粘弹性数值模拟龙门山断裂带应力积累及大震复发周期   总被引：4，自引：0，他引：4  
柳畅  朱伯靖  石耀霖 《地质学报》2012,86(1):157-169
2008年5月12日在低地形变速率的龙门山断裂带上突发汶川强震,引发人们对该地震孕震机制的思考。本文根据GPS观测资料确定边界条件,通过三维粘弹性数值模拟探讨了汶川地震的孕震机理,计算了该区域岩石圈的应力增加速率和积累过程,以及汶川地震同震应力变化与震后应力松弛,在此基础上估算了汶川8.0级大地震的复发周期。数值模拟结果表明:印度板块对欧亚板块的推挤造成青藏高原的物质东流,高原中、下地壳物质在龙门山断裂带处遭到相对坚硬的四川盆地的阻挡之后,部分中、下地壳物质在龙门山断裂带下堆积产生应力集中。两个重要因素为应力集中提供了重要控制作用:其一是青藏高原中、下地壳较低的粘滞系数与四川盆地中、下地壳较高的粘滞系数的差异,其二是从青藏高原到四川盆地的Moho面深度在龙门山断裂带的突变。低应变速率的龙门断裂带岩石圈在数千年时间尺度的应力积累过程中,脆性上地壳的应力随时间近乎线性增长,并且上地壳深部的应力增长率超过浅部,6000年内应力积累最大量达到-21.6MPa,应力增长速率为-0.0036MPa/a;而柔性的中、下地壳以及岩石圈上地幔的应力在增长一段时间之后趋于稳定。在空间上,龙门山断裂带受到的压应力从断层西南向北东方向逐渐减小,而剪应力从西南到北东方向逐渐增大,应力状态有利于地震发生时断层的破裂方式从西南的逆冲运动向北东的逆冲兼走滑运动的方式发展。通过应力积累与地震应力降的计算得到汶川8.0级大地震的复发周期约为5400年。  相似文献   

14.
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   


15.
Sargeant  S.L.  Burton  P.W.  Douglas  A.  Evans  J.R. 《Natural Hazards》2002,27(1-2):35-45
On 7 September, 1999, an earthquake (5.8 mb USGS)took place about 20 km from the centre of Athens, until then a seismically quiet region ofeastern Greece. Considerable damage ranging from rock falls to the collapse of reinforcedconcrete structures was reported in the city and surrounding area. No surface break which couldbe directly attributed to rupture on the fault plane was mapped. We use the relativeamplitude method and forward modelling of broadband P seismogramsrecorded at long range to produce a two-dimensional model of the source. We conclude that the earthquake tookplace on a south-west dipping normal fault at a depth of 10 km. This implies that the depthof the seismogenic zone in the area is comparable to other more active regions of Greece.The rupture speed (2.1 km/s) and stress drop (0.54 MPa) are low and are typical of earthquakesin a tectonic environment dominated by high rates of extension. The estimated seismicmoment is 6.014 × 1017 N m. We have investigated reported rupture directivity and thepossibility of a circular rupture is also examined. Extrapolation of the fault plane to the freesurface suggests that the earthquake took place on a structure associated with the Fili fault.  相似文献   

16.
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   

17.
A three-dimensional local-scale P-velocity model down to 25 km depth around the main shock epicenter region was constructed using 83821 event-to-receiver seismic rays from 5856 aftershocks recorded by a newly deployed temporary seismic network.Checkerboard tests show that our tomographic model has lateral and vertical resolution of～2 km.The high-resolution P-velocity model revealed interesting structures in the seismogenic layer:(1) The Guanxian-Anxian fault, Yingxiu-Beichuan fault and Wenchuan-Maoxian f...  相似文献   

18.
Earthquakes in SE Australia are usually caused by compressive stresses acting in the crust, and are associated with steeply dipping faults. Sometimes the faulting is predominantly strike‐slip, as for the Bowning earthquakes of 1977 and some of the Dalton/Gunning earthquakes; and sometimes it is high‐angle thrust faulting, as for the 1961 Robertson and 1973 Picton earthquakes. No surface expression of the faults associated with any recent earthquakes in SE Australia has been reported.

The directions of the pressure axes, from all the earthquakes for which focal mechanisms have been determined, do not form a consistent pattern. This suggests that the faulting associated with earthquakes in SE Australia is dominated by the geometry of pre‐existing crustal faults or zones of weakness.

In situ stress measurements have not been made near the epicentral areas of the larger recent earthquakes, because of the absence of competent, near‐surface rocks coupled to the crust. However, in the western part of the Lachlan Fold Belt the in situ stress results indicate that the maximum pressure axis is approximately E‐W. The evidence from the focal mechanisms does not preclude the persistence of this stress regime farther to the east, and a regional compressive stress in the crust with an azimuth of about 120° is consistent with most of the earthquake focal mechanisms and the in situ stress measurements throughout SE Australia.  相似文献   

19.
《International Geology Review》2012,54(12):1129-1144
Groups of grabens in west Anatolia have contrasting E-W and NE-SW orientations and are the subject of debate as to their relative ages and relationships. We investigated the E-W-trending Gediz graben and its neighboring NE-SW-trending Gördes, Demirci, and Selendi grabens, which form an important graben system representative of the region. We studied gravity data from one profile and magnetotelluric (MT) data from two profiles, 73 km and 93 km long. The data supports the hypothesis that the Gediz graben was superimposed onto the (older) NE-SW grabens. 2D gravity and MT modelling revealed an undulating graben floor, varying in depth between 500 and 3000-4000 m (gravity-MT); within the graben two apparent basins 3–4 and 1.5-2.5 km deep (gravity-MT) are separated by a subsurface horst. The residual gravity map appears to indicate the continuation of NE-SW grabens from north of Gediz graben to beyond its southern border.

The MT model revealed three main zones of varying thickness within the crust. The britde upper crust comprises two zones: sedimentary fill (apparent resistivity 15-50 ohm.m) and Menderes massif basement (200 ohm.m). The third zone is highly conductive lower crust (10 ohm.m), identified by our MT modeling at an average depth of 10 km. This conductive layer was considered in conjunction with two other regional features, high heat flow values and shallow earthquake focal depths. A heat flow map shows a very high average value of 108 mWm?2 for west Anatolia and 120-300 mWm?2 for the Gediz graben area specifically, compared with the world average of 80 mWm?2. Seismological records showing shallow earthquake focal depths together with the high conductivity zone were taken to indicate a partially melted, viscoelastic lower crust.  相似文献   

20.
THE ORIGIN OF DOUBLE HIGH CONDUCTIVITY LAYERS IN THE CRUST OF SOUTHERN TIBET AND ITS GEODYNAMIC CONSEQUENCE  相似文献   

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