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1.
Modern tectonic stress field in the Chinese mainland inverted from focal mechanism solutions 总被引:1,自引:0,他引:1
IntroductionTheinversionapproachofregionalstressfielddevelopedinrecent10to20yearsprovidesausefultoolforstudyingthemeanstressinagivenregion(Angeller,1979;Ellsworth,1981,Xu,Ge,1984).Becauseitusesmultitudinousfaultsinsteadofsinglefault,itcanremovetheinhomogeneityoflocalmediumsoastorevealtheregionalstressinformation.Besides,thismethodproducesaRvalue,whichisdefinedby(O-2--q)/(q--q),andmaydescribestherelativemagnitUdeofintermediateprincipalstress,whereq,acand%arethemaximum,theintermediateandthemi… 相似文献
2.
Giuseppe Pasquale Raffaella De Matteis Annalisa Romeo Rosalba Maresca 《Journal of Seismology》2009,13(1):107-124
The goal of this study was to estimate the stress field acting in the Irpinia Region, an area of southern Italy that has been
struck in the past by destructive earthquakes and that is now characterized by low to moderate seismicity. The dataset are
records of 2,352 aftershocks following the last strong event: the 23 November 1980 earthquake (M 6.9). The earthquakes were
recorded at seven seismic stations, on average, and have been located using a three-dimensional (3D) P-wave velocity model
and a probabilistic, non-linear, global search technique. The use of a 3D velocity model yielded a more stable estimation
of take-off angles, a crucial parameter for focal mechanism computation. The earthquake focal mechanisms were computed from
the P-wave first-motion polarity data using the FPFIT algorithm. Fault plane solutions show mostly normal component faulting
(pure normal fault and normal fault with a strike-slip component). Only some fault plane solutions show strike-slip and reverse
faulting. The stress field is estimated using the method proposed by Michael (J Geophys Res 92:357–368, 1987a) by inverting selected focal mechanisms, and the results show that the Irpinia Region is subjected to a NE–SW extension with
horizontal σ
3 (plunge 0°, trend 230°) and subvertical σ
1 (plunge 80°, trend 320°), in agreement with the results derived from other stress indicators. 相似文献
3.
Prantik Mandal 《Pure and Applied Geophysics》2008,165(7):1307-1324
Double difference relocations of the 1402 Kachchh events (2001–2006) clearly delineate two fault zones viz. south-dipping
North Wagad fault (NWF) and almost vertical Gedi fault (GF). The relocated focal depths delineate a marked variation of 4
and 7 km in the brittle-ductile transition depths beneath GF and NWF, respectively. The focal mechanism solutions of 464 aftershocks
(using 8–12 first motions) show that the focal mechanisms ranged between pure reverse and pure strike-slip except for a few
pure dip-slip solutions. The stress inversions performed for five rectangular zones across the Kachchh rift reveal both clockwise
and anticlockwise rotation (7–32°) in the σ1 orientation within the rupture zone, favoring a heterogeneous stress regime with an average N-S fault normal compression.
This rotation may be attributed to the presence of crustal mafic intrusives (5–35 km depth) in the rupture zone of the 2001
Bhuj main shock. Results suggest a relatively homogeneous stress regime in the GF zone favoring strike-slip motion, with a
fault normal N-S compression. 相似文献
4.
We determine the stress field of Guangdong and its adjacent area by using focal mechanism solutions of 137 earthquakes and obtain tectonic stress tensors in 12 zones. The result shows that the azimuth of maximum principal stress σ1 is approximately WNW in southwestern Fujian, southern Jiangxi, Guangdong’s Heyuan and the Pearl River Delta, NW in Guangdong’s Yangjiang, and nearly NNW in the two zones of eastern Guangxi and Beibuwan Gulf (the Northern Gulf), varying clockwise in WNW-NW-NNW from east to west. The azimuth of minimum principal stress σ3 varies from NNE to ENE. The relative magnitude of medium principal stress σ2 (R value), is the smallest in Beibuwan and largest in Longyan of Fujian. Strike-slip faulting is dominated in the study area. 相似文献
5.
Suha Ozden Semir Over Kaan Sevki Kavak Serife Sevinc Inal 《Journal of Geodynamics》2008,46(1-2):48-62
This study defines the Late Cenozoic stress regimes acting around the Bolu Basin along the North Anatolian Fault in northwestern Turkey. The inferred regional stress regime, obtained from the inversion of measured fault-slip vectors as well as focal mechanism solutions, is significant and induces the right-lateral displacement of the North Anatolian Fault. The field observations have also revealed extensional structures in and around the Bolu Basin. These extensional structures can be interpreted as either a local effect of the regional transtensional stress regime or as the result of the interaction of the fault geometries of the dextral Duzce Fault and the southern escarpment of the North Anatolian Fault, bordering the Bolu Basin in the north and in the south, respectively.The inversion of slip vectors measured on fault planes indicates that a strike-slip stress regime with consistent NW- and NE-trending σHmax(σ1) and σHmin(σ3) axes is dominant. Stress ratio (R) values provided by inversion of slip vectors measured on both major and minor faults and field observations show significant variations of principal stress magnitudes within the strike-slip stress regime resulting in older transpression to younger transtension. These two stress states, producing dextral displacement along NAF, are coaxial with a consistent NE-trending σ3 axis. The earthquake focal mechanism inversions confirm that the transtensional stress regime has continued into recent times, having identical horizontal stress axis directions, characterized by NW and NE-trending σ1 and σ3 axes, respectively. A locally consistent NE-trending extensional, normal faulting regime is also seen in the Bolu Basin. The stress-tensor change within the strike-slip stress regime can be explained by variations in horizontal stress magnitudes that probably occurred in Quaternary times as a result of the westward extrusion of the Anatolian block. 相似文献
6.
Haluk Ozener Esen Arpat Semih Ergintav Asli Dogru Rahsan Cakmak Bulent Turgut Ugur Dogan 《Journal of Geodynamics》2010,49(3-4):141-150
The North Anatolian Fault Zone (NAFZ), which marks the boundary between Anatolia and the Eurasian plate, is one of the world's most seismically active structures. Although the eastern part of NAFZ has high seismic hazard, there is a lack of geodetic information about the present tectonics of this region. Even though many scientists would like to study this area, geographical and logistical problems make performing scientific research difficult. In order to investigate contemporary neotectonic deformation on the eastern NAFZ and in its neighborhood, a relatively dense Global Positioning System (GPS) monitoring network was established in 2003. Geodetic observations were performed in three GPS campaigns in an area of 350 km × 200 km with 12-month intervals. In addition, 14 new GPS stations were measured far from the deforming area. Since this region includes the intersection of the NAFZ and the East Anatolian Fault Zone (EAFZ), deformation is complex and estimating seismic hazard is difficult. One important segment is the Yedisu segment and it has not broken since the 1784 earthquake. After the 1992 Erzincan and 2003 Pulumur earthquakes, the Coulomb stress loading on the Yedisu segment of the NAFZ has increased significantly, emphasizing the need to monitor this region. We computed the horizontal velocity field with respect to Eurasia and strain rates field as well. GPS-derived velocities relative to Eurasia are in the range of 16–24 mm/year, which are consistent with the regional tectonics. The principal strain rates were derived from the velocity field. Results show that strain is accumulating between the NAFZ and EAFZ along small secondary fault branches such as the Ovacik Fault (OF). 相似文献
7.
I. B. Boikov M. V. Kravchenko V. I. Kryuchko 《Izvestiya Physics of the Solid Earth》2010,46(4):339-349
Numerical algorithms are suggested for reconstructing the potential field in the region Ω = {0 ≤ R
0 ≤ ρ ≤ R, 0 ≤ θ ≤ π, 0 ≤ φ ≤ 2π} from its values on the surface Γ1 = {R,0 ≤ α1 ≤ θ ≤ α2 ≤ π, 0 ≤ β1 ≤ φ ≤ β2 ≤ π}. 相似文献
8.
EstimationofseismicstresdropfromthepeakvelocityofgroundmotionJIAZHENGQIN(秦嘉政)ZUYINLIU(刘祖荫)XIAODONGQIAN(钱晓东)QINGYINXIE(谢庆... 相似文献
9.
Types of focal mechanism solutions and parameter consistency of the sub-blocks in Sichuan and Yunnan Provinces 总被引:1,自引:0,他引:1
Based on P- and S-wave amplitudes and some clear initial P-wave motion data, we calculated focal mechanism solutions of 928 M≥2.5 earthquakes (1994-2005) in four sub-blocks of Sichuan and Yunnan Provinces, namely Sichuan-Qinghai, Yajiang, Central Sichuan and Central Yunnan blocks. Combining these calculation results with those of the focal mechanism solutions of moderately strong earthquakes, we analyzed the stress field characteristics and dislocation types of seismogenic faults that are distributed in the four sub-blocks. The orientation of principal compressive stress for each block is: EW in Sichuan-Qinghai, ESE or SE in Yajiang, Central Sichuan and Central Yunnan blocks. Based on a great deal of focal mechanism data, we designed a program and calculated the directions of the principal stress tensors, σ1, σ2 and σ3, for the four blocks. Meanwhile, we estimated the difference (also referred to as consistency parameter θ^- ) between the force axis direction of focal mechanism solution and the direction of the mean stress tensor of each block. Then we further analyzed the variation of θ^- versus time and the dislocation types of seismogenic faults. Through determination of focal mechanism solutions for each block, we present information on the variation in θ^- value and dislocation types of seismogenic faults. 相似文献
10.
A catalog for northeast India and the adjoining region for the period 1897–2009 with 4,497 earthquakes events is compiled
for homogenization to moment magnitude M
w,GCMT in the magnitude range 3–8.7. Relations for conversion of m
b and M
s magnitudes to M
w,GCMT are derived using three different methods, namely, linear standard regression, inverted standard regression (ISR) and orthogonal
standard regression (OSR), for different magnitude ranges based on events data for the catalog period 1976–2006. The OSR relations
for M
s to M
w,GCMT conversion derived in this paper have significantly lower errors in regression parameters compared to the relations reported
in other studies. Since the number of events with magnitude ≥7 for this region is scanty, we, therefore, considered whole
India region to obtain the regression relationships between M
w,GCMT and M
s,ISC. A relationship between M
w,GCMT and M
w,NEIC is also obtained based on 17 events for the range 5.2 ≤ magnitude ≤ 6.6. A unified homogeneous catalog prepared using the
conversion relations derived in this paper can serve as a reference catalog for seismic hazard assessment studies in northeast
India and the adjoining region. 相似文献
11.
In this study we investigate present-day seismicity and crustal deformation of Egypt based on a comprehensive earthquake catalog
from 1900 to 2004 by focal mechanism stress inversion and by recent GPS observations. Spatial distribution of earthquake epicenters
indicates that Egypt has been suffered from both interplate and intraplate earthquakes. Most earthquake activity (more than
70%) has been concentrated in northern Egypt along the geologically documented borders of Sinai subplate (northern Red Sea
and its two branches Suez rift and Aqaba–Dead Sea transform). The majority of inland earthquake focal mechanisms in Egypt
are normal with strike-slip component or strike-slip faulting events. Only a small minority, namely four events, exhibits
reverse faulting. The inversion method of Gephart and Forsyth (1984) was applied to calculate the orientation of the principle
stress axes and the shape of the stress tensor. The best fitting tensor in Egypt shows homogeneity stress field. The tension
stress regime is dominant in northern Egypt. The stress directions are well resolved by the 95% confidence limits, the relative
stress magnitude has a value of about 0.3. However, along southern Egypt the strike-slip regime is dominant. The shape factor
(R-value) is 0.5, which means that the deviatoric components of σ1 and σ3 are of the same magnitude, but of opposite signs. The average horizontal velocity of GPS stations in Egypt is 5.15± 1.1 mm/year
in mostly NNW direction. The results of deformation analysis indicate that the northern Egypt is deformed more than the southern
part. Only the Egyptian-Mediterranean coastal–Nile Delta zone dominates as a compression deformation area. However, an extensional
deformation has been observed throughout the rest of country. This means that the relative motion of African plate with respect
to both Eurasian and Arabian has highly controlled the deformation processes in Egypt. 相似文献
12.
On the basis of about 300 earthquake wave forms observed in the Shidian M
S=5.9 sequences on April 12, 2001 recorded in Kunming Digital Seismic Network, the spectra of shear wave have been used to
estimate the focal parameters of these earthquake sequences. The results show that within the magnitude range of 1.5–5.3,
the seismic moments are 1010–1016 N·m, the corner frequencies are 0.2–0.8 Hz, radii of the focal rupture are 200–2 500 m and the stress drops are 0.1×105–20×105Pa. Through the statistical analyses of variation of corner frequency f
c and stress drop Δσ with time, it is discovered that the average corner frequency of the foreshock sequences is obviously
lower than that of the aftershock sequences. Contrarily, the average stress drops Δσ of the foreshock sequences are clearly
higher than that of the aftershocks. It is considered that these variation characteristics of average corner frequency and
stress drops before and after the main shock have index significance to the precursory information before a strong earthquake.
The higher stress drops for the foreshock sequences show that the higher shear stresses have been stored in the area of main
shock. After the main shock, most of the stresses have been released, so the aftershock sequences show a rupture process of
lower stresses.
Foundation item: Scientific and Technological Key Project of Yunnan Province (2001NG46) 相似文献
13.
Characteristicsofambientstressvaluesformicro-earthquakesequencesinWesternYunnan Earthquake Prediction Experimental FieldJia-Z... 相似文献
14.
Monitoring the West Bohemian earthquake swarm in 2008/2009 by a temporary small-aperture seismic array 总被引:1,自引:1,他引:0
The most recent intense earthquake swarm in West Bohemia lasted from 6 October 2008 to January 2009. Starting 12 days after
the onset, the University of Potsdam monitored the swarm by a temporary small-aperture seismic array at 10 km epicentral distance.
The purpose of the installation was a complete monitoring of the swarm including micro-earthquakes (M
L < 0). We identify earthquakes using a conventional short-term average/long-term average trigger combined with sliding-window
frequency-wavenumber and polarisation analyses. The resulting earthquake catalogue consists of 14,530 earthquakes between
19 October 2008 and 18 March 2009 with magnitudes in the range of − 1.2 ≤ M
L ≤ 2.7. The small-aperture seismic array substantially lowers the detection threshold to about M
c = − 0.4, when compared to the regional networks operating in West Bohemia (M
c > 0.0). In the course of this work, the main temporal features (frequency–magnitude distribution, propagation of back azimuth
and horizontal slowness, occurrence rate of aftershock sequences and interevent-time distribution) of the recent 2008/2009
earthquake swarm are presented and discussed. Temporal changes of the coefficient of variation (based on interevent times)
suggest that the swarm earthquake activity of the 2008/2009 swarm terminates by 12 January 2009. During the main phase in
our studied swarm period after 19 October, the b value of the Gutenberg–Richter relation decreases from 1.2 to 0.8. This trend is also reflected in the power-law behavior
of the seismic moment release. The corresponding total seismic moment release of 1.02×1017 Nm is equivalent to M
L,max = 5.4. 相似文献
15.
Zafeiria Roumelioti Anastasia Kiratzi Christoforos Benetatos 《Journal of Seismology》2010,14(2):309-337
We use 576 earthquakes of magnitude, M
w, 3.3 to 6.8 that occurred within the region 33° N–42.5° N, 19° E–30° E in the time period 1969 to 2007 to investigate the
stability of the relation between moment magnitude, M
w, and local magnitude, M
L, for earthquakes in Greece and the surrounding regions. We compare M
w to M
L as reported in the monthly bulletins of the National Observatory of Athens (NOA) and to M
L as reported in the bulletins of the Seismological Station of the Aristotle University of Thessaloniki. All earthquakes have
been analyzed through regional or teleseismic waveform inversion, to obtain M
w, and have measured maximum trace amplitudes on the Wood–Anderson seismograph in Athens, which has been in operation since
1964. We show that the Athens Wood–Anderson seismograph performance has changed through time, affecting the computed by NOA
M
L by at least 0.1 magnitude units. Specifically, since the beginning of 1996, its east–west component has been recording systematically
much larger amplitudes compared to the north–south component. From the comparison between M
w and M
L reported by Thessaloniki, we also show that the performance of the sensors has changed several times through time, affecting
the calculated M
L’s. We propose scaling relations to convert the M
L values reported from the two centers to M
w. The procedures followed here can be applied to other regions as well to examine the stability of magnitude calculations
through time. 相似文献
16.
G. Ameri A. Oth M. Pilz D. Bindi S. Parolai L. Luzi M. Mucciarelli G. Cultrera 《Bulletin of Earthquake Engineering》2011,9(3):717-739
We exploit S-wave spectral amplitudes from 112 aftershocks (3.0 ≤ ML ≤ 5.3) of the L’Aquila 2009 seismic sequence recorded at 23 temporary stations in the epicentral area to estimate the source
parameters of these events, the seismic attenuation characteristics and the site amplification effects at the recording sites.
The spectral attenuation curves exhibit a very fast decay in the first few kilometers that could be attributed to the large
attenuation of waves traveling trough the highly heterogeneous and fractured crust in the fault zone of the L’Aquila mainshock.
The S-waves total attenuation in the first 30 km can be parameterized by a quality factor QS(f) = 23f
0.58 obtained by fixing the geometrical spreading to 1/R. The source spectra can be satisfactorily modeled using the omega-square
model that provides stress drops between 0.3 and 60 MPa with a mean value of 3.3±2.8 MPa. The site responses show a large
variability over the study area and significant amplification peaks are visible in the frequency range from 1 to more than
10 Hz. Finally, the vertical component of the motion is amplified at a number of sites where, as a consequence, the horizontal-to-vertical
spectral ratios (HVSR) method fails in detecting the amplitude levels and in few cases the resonance frequencies. 相似文献
17.
Direction and structure characteristics of 58 tectonic stress tensors have been determined in 41 surveyed areas (points) in
the southwestern district of China through a calculation method for inversion of tectonic stress tensors from sliding direction
of faults, and, in combination with seismic mechanism solution andin-situ stress measurements, the following characteristics of the recent tectonic stress fields in the southwestern district of China
have been defined: (1) the stress fields in this district have remained stable since the end of early to mid-Pleistocene;
(2) the effect of such tectonic stresses is mainly horizontal; (3) the orientation of the maximum principal stress axis shows
a trend of regular rotation from north to south, i. e. from NEE-SWW in northern Songpan and Longmen Shan areas to sub-EW in
the central part of western Sichuan, and further to NNW-SWW or sub-SN in Yunnan; (4) the regional tectonic stress fields are
of distinct division character; (5) there is well concordance between the main direction and type of stress structures in
the stress tate both in deep and shallow parts of the crust. In addition, studies of staged tectonic stress tensors preliminarily
show that in early Quaternary the southwestern district was mainly affected by lateral compression of Indian plate, under
which the regional tectonic stress fields mainly display NE-sub-EW compression.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 407–417, 1993. 相似文献
18.
Prediction of rockburst probability given seismic energy and factors defined by the expert method of hazard evaluation (MRG) 总被引:2,自引:0,他引:2
In this paper we suggest that conditional estimator/predictor of rockburst probability (and rockburst hazard, P
T
(t)) can be approximated with the formula P
T
(t) = P
1(θ
1)…P
N
(θ
N
)·P
dyn
T
(t), where P
dyn
T
(t) is a time-dependent probability of rockburst given only the predicted seismic energy parameters, while P
i
(θ
i
) are amplifying coefficients due to local geologic and mining conditions, as defined by the Expert Method of (rockburst)
Hazard Evaluation (MRG) known in the Polish mining industry. All the elements of the formula are (approximately) calculable
(on-line) and the resulting P
T
value satisfies inequalities 0 ≤ P
T
(t) ≤ 1. As a result, the hazard space (0–1) can be always divided into smaller subspaces (e.g., 0–10−5, 10−5–10−4, 10−4–10−3, 10−3–1), possibly named with symbols (e.g., A, B, C, D, …) called “hazard states” — which saves the prediction users from worrying of probabilities. The estimator P
T
can be interpreted as a formal statement of (reformulated) Comprehensive Method of Rockburst State of Hazard Evaluation,
well known in Polish mining industry. The estimator P
T
is natural, logically consistent and physically interpretable. Due to full formalization, it can be easily generalized, incorporating
relevant information from other sources/methods. 相似文献
19.
InfluencecausedbyinitialtectonicstresonrelativemeasurementofboreholegroundstresinviscoelasticmediaPENG-JUNZHAO1)(赵鹏君),JIAN-W... 相似文献
20.
Alignmentsilkwormsasseismicanimalanomalousbehavior(SAAB)andelectromagneticmodelofafault:atheoryandlaboratoryexperimentMOTO... 相似文献