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1.
The source parameters of the M
W
= 7.6 Olyutorskii earthquake were estimated using the moments of the slip rate function with degrees 1 and 2. The moments
were estimated from broadband P-wave records at 52 stations of the worldwide network. The first step was to find a function S(t) for each station; this function is an apparent source time function, i.e., the P-wave slip as radiated by the source toward a station under consideration. The method of empirical Green’s functions was used
to estimate S(t). The next step was to calculate the moments of S(t) of degrees 1 and 2 over time and to set up relevant equations to be solved by least squares for the unknown source moments.
The horizontal linear source was used as a nonparametric model for calculating the source moments. Haskell’s parametric model
was used for further interpretation of the source moments. The resulting estimates are as follows: the source centroid was
13–25 km southwest of the epicenter, the source was 105–120 km long, the source strike was 222°–228°, the rupture velocity
was 2.7–3.0 km/s, and the total radiation duration was 24–27 s. These estimates indicate a bilateral rupture dominated by
a southwestward sense of rupture propagation. The source characteristics are consistent with the aftershock area geometry
and with the focal mechanism, as well as with surface breakage as observed by geologists in the field. 相似文献
2.
William Menke Hannah Abend Dalia Bach Kori Newman Vadim Levin 《Surveys in Geophysics》2006,27(6):603-613
The December 26, 2004 Sumatra–Andaman Island earthquake, which ruptured the Sunda Trench subduction zone, is one of the three largest earthquakes to occur since global monitoring began in the 1890s. Its seismic moment was M
0 = 1.00 × 1023–1.15 × 1023 Nm, corresponding to a moment-magnitude of M
w
= 9.3. The rupture propagated from south to north, with the southerly part of fault rupturing at a speed of 2.8 km/s. Rupture propagation appears to have slowed in the northern section, possibly to ∼2.1 km/s, although published estimates have considerable scatter. The average slip is ∼5 m along a shallowly dipping (8°), N31°W striking thrust fault. The majority of slip and moment release appears to have been concentrated in the southern part of the rupture zone, where slip locally exceeded 30 m. Stress loading from this earthquake caused the section of the plate boundary immediately to the south to rupture in a second, somewhat smaller earthquake. This second earthquake occurred on March 28, 2005 and had a moment-magnitude of M
w
= 8.5. 相似文献
3.
On July 20, 1995, an earthquake of M
L=4.1 occurred in Huailai basin, northwest of Beijing, with epicenter coordinates 40.326°N, 115.448°E and focal depth 5.5 km.
Following the main shock, seismicity sharply increased in the basin. This earthquake sequence was recorded by Sino-European
Cooperative Huailai Digital Seismograph Network (HDSN) and the hypocentres were precisely located. About 2 hours after the
occurrence of the main shock, a smaller event of M
L=2.0 took place at 40.323°N, 115.447°E with a focal depth of 5.0 km, which is very close to the main shock. Using the M
L=2.0 earthquake as an empirical Green’s function, a regularization method was applied to retrieve the far-field source-time
function (STF) of the main shock. Considering the records of HDSN are the type of velocity, to depress high frequency noise,
we removed instrument response from the records of the two events, then integrated them to get displacement seismogram before
applying the regularization method. From the 5 field stations, P phases in vertical direction which mostly are about 0.5 s
in length were used. The STFs obtained from each seismic phases are in good agreement, showing that the M
L=4.1 earthquake consisted of two events. STFs from each station demonstrate an obvious “seismic Doppler effect”. Assuming
the nodal plane striking 37° and dipping 40°, determined by using P wave first motion data and aftershock distribution, is
the fault plane, through a trial and error method, the following results were drawn: Both of the events lasted about 0.1 s,
the rupture length of the first one is 0.5 km, longer than the second one which is 0.3 km, and the rupture velocity of the
first event is 5.0 km/s, larger than that of the second one which is about 3.0 km/s; the second event took place 0.06 s later
than the first one; on the fault plane, the first event ruptured in the direction γ=140° measured clockwise from the strike
of the fault, while the second event ruptured at γ=80°, the initial point of the second one locates at γ=−100° and 0.52 km
from the beginning point of the first one. Using far-field ground displacement spectrum measurement method, the following
source parameters about the M
L=4.1 earthquake were also reached: the scalar earthquake moment is 3.3×1013 N·m, stress drop 4.6 MPa, rupture radius 0.16 km.
Contribution No. 99FE2022, Institute of Geophysics, China Seismological Bureau.
This study is supported by the Chinese Joint Seismological Science Foundation (95-07-411). 相似文献
4.
The paper presents some results of seismic experiments carried out on the territory of northern Moravia and Silesia, roughly
delimited by the coordinates 16°E–19°E and 49°N–51°N. The experiments were aimed at compiling a velocity model of the uppermost
Earth’s crust using the database of arrival times of Pg and Sg waves recorded at a fairly large number of seismic stations, which enabled us to produce a simple 1D-layered velocity model
of the region. The velocity model was computed using the traditional tomographic iterative process composed of consecutive
solutions of linear equations. Based on the analysis of velocity distribution, it was found that the velocities of Pg and Sg waves increase from about 5.9 and 3.3 km/s at the surface, to about 6.1 and 3.5 km/s at a depth of 11 km, respectively. 相似文献
5.
Frequency analysis of the Sumatra-Andaman earthquake of 2004, one of the most significant and best-recorded earthquakes, is
based on spectral seismograms obtained from their broadband seismograms. The Sumatra-Andaman earthquake is found to have a
wide-range frequency content of P-wave radiation during the rupturing process. On the basis of stacking spectral seismograms
we distinguished four time events of the rupturing process of a total length of about 540 s. The frequency, f
max, is the highest for the first event (0.163 Hz in time interval 0–88 s), lowest for the second — which is the strongest (0.075
Hz in time interval 88–204 s). For third and fourth events frequencies are similar (0.089 and 0.082 Hz in time intervals 204–452
and 452–537 s, respectively). The frequency also shows an azimuthal dependence (±0.02 Hz). Azimuths for which the frequency,
f
max, has maximum and minimum values are 203–222° and 23–42°, respectively. These observations are discussed in relation to previously
published papers on this topic. 相似文献
6.
The source parameters of the Bohai Sea earthquake, July 18, 1969 and Yongshan, Yunnan earthquake, May 11, 1974 were determined
by full — wave theory synthetic seismograms of teleseismic P waves. P+pP+sP wereform were calculated with WKBJ approximation
and real integral paths. One — dimensional unilateral, finite propagation source was also considered. By trail — and — error
in comparing the theoretical seismograms with the observational ones of WWSSN stations, the source parameters were obtained
as follow: for Bohai earthquake, φ=195°, δ=85°, λ=65°,M
o=0.9×1019Nm,L=59.9km.V
R=3.5km/s, ∧
R
=160°; for Yongshan earthquake, φ=240°, δ=80°, ∧=150°,M
o=1.3×1018Nm,L=48.8km,V
R=3km/s, ∧
R
=−10°, where φ is strike, δ dip angle, λ slip angle,M
o seismic moment,L rupture length,V
R rupture propagation speed. As III type fractures the faulting propagated along the fault planes, and ∧
R
is the angle from the strike to the propagation direction. Yongshan earthquake showed complexity in its focal process, having
four sub—ruptures during the first 60 seconds.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 1–8, 1991. 相似文献
7.
LIU Rui-feng CHEN Yun-tai Frank Krueger CHENG Jin YANG Hui HAN Wei MOU Lei-yu 《地震学报(英文版)》2000,13(3):241-248
Breakthrough point source model, extended earthquake source model is used to calculate more seismic source parameters in this paper. We express seismic source using higher degree moment tensors, to reduce a large number terms originally presenting in higher degree moment tensor representation, Haskell rupture model is used. We inverted the source parameters of Mani earthquake in Tibet using broad-band body wave of 32 stations of Global Seismograph Network (GSN), the results show that it is a strike-slip fault, rupture direction is 75° , rupture duration is 19 s, the fault plan is f =77° , d =88° , l =0° , the auxiliary plane is f =347° , d =90° , l =178° , and the fault dimension is 47 km′ 28 km. These results will give new quantitative data for earth dynamics and have practical meaning for seismic source tomography research. 相似文献
8.
Prantik Mandal R K Chadha C Satyamurty I P Raju N Kumar 《Pure and Applied Geophysics》2005,162(12):2479-2504
Site response in the aftershock zone of 2001 Bhuj Mw 7.7 earthquake has been studied using the H/V spectral ratio method using 454 aftershocks (Mw 2.5–4.7) recorded at twelve three-component digital strong motion and eight three-component digital seismograph sites. The
mean amplification factor obtained for soft sediment sites (Quaternary/Tertiary) varies from 0.75–6.03 times for 1–3 Hz and
0.49–3.27 times for 3–10 Hz. The mean amplification factors obtained for hard sediment sites (hard Jurassic/Mesozoic sediments)
range from 0.32–3.24 times for 1–3 Hz and 0.37–2.18 times for 310 Hz. The upper bounds of the larger mean amplification factors
for 1–3 Hz are found to be of the order of 3.13–6.03 at Chopadwa, Vadawa, Kavada, Vondh, Adhoi, Jahwarnagar and Gadhada, whereas,
the upper bounds of the higher mean amplification factors at 3–10 Hz are estimated to be of the order of 2.00–3.27° at Tapar,
Chopadwa, Adhoi, Jahwarnagar, Gandhidham and Khingarpur. The site response estimated at Bhuj suggests a typical hard-rock
site behavior. Preliminary site response maps for 1–3 Hz and 310 Hz frequency ranges have been prepared for the area extending
from 23–23.85 °N and 69.65–70.85°E. These frequency ranges are considered on the basis of the fact that the natural frequencies
of multi-story buildings (3 to 10 floor) range between 1–3 Hz, while the natural frequencies for 1 to 3 story buildings vary
from 3–10 Hz. The 1–3 Hz map delineates two distinct zones of maximum site amplification (>3 times): one lying in the NW quadrant
of the study area covering Jahwarnagar, Kavada and Gadadha and the other in the SE quadrant of the study area with a peak
of 6.03 at Chopadwa covering an area of 70 km × 50 km. While the 3–10 Hz map shows more than 2 times site amplification value
over the entire study area except, NE quadrant, two patches in the southwest corner covering Bhuj and Anjar, and one patch
at the center covering Vondh, Manfara and Sikara. The zones for large site amplification values (∼3 times) are found at Tapar,
Chopadwa, Adhoi and Chobari. The estimated site response values show a good correlation with the distribution of geological
formations as well as observed ground deformation in the epicentral zone. 相似文献
9.
Ihsane Bensaid Taj-Eddine Cherkaoui Fida Medina Bento Caldeira Elisa Buforn Anas Emran Youssef Hahou 《Journal of Seismology》2012,16(1):35-53
The Tafilalt region, located at the eastern end of the Anti-Atlas chain in Morocco, was shaken on 23 and 30 October 1992 by
two moderate earthquakes of magnitude mb ∼ 5 and intensity ∼ VI MSK64, which caused two deaths and great damage in the area between Erfoud and Rissani. The review
of data available on the seismic crisis allowed us to improve the knowledge on the macroseismic, instrumental and source parameters
of the earthquakes. The main results of the present study are: (1) location of the epicentres with the help of data from a
close portable network allowed us to propose new epicentral coordinates at 31.361° N, 4.182° W (23 October) and 31.286° N,
4.347° W (30 October); both events have focal depths of 2 km; (2) the shock of 30 October was followed by a series of 305
aftershocks, most of which were located west of Rissani; the 61 best-constrained events had focal depths of 5 to 19 km and
magnitudes 0.7 to 3; (3) the largest damage was located in an area between the two epicentres within the Tafilalt valley and
was probably amplified by site effects due to the proximity of the water table within the Quaternary sediments; (4) focal
mechanisms of the main events correspond to strike-slip faulting with fault planes oriented N–S (left lateral) and E–W (right
lateral); the only mechanism available for the aftershocks also corresponds to strike-slip faulting; (5) spectral analysis
shows that the scalar seismic moment (Mo) of the first event is slightly larger than the second; the corresponding values of Mw are 5.1 and 5.0, respectively; (6) the dimensions of the faults for a circular fault model are 7.7 ± 1.4 and 7.4 ± 1.2 km,
respectively; the average displacement is 4 cm for the first event and 3.7 cm for the second; the stress drop is 0.4 and 0.3 MPa,
respectively, in agreement with standard values; (7) the Coulomb Stress test performed for both earthquakes suggests a relationship
between both events only when the used location is at the limit of the horizontal uncertainty; (8) finally, the occurrence
of these shocks suggests that the Anti-Atlas is undergoing tectonic deformation in addition to thermal uplift as suggested
by recent publications. 相似文献
10.
IntroductionSince the late 1970s, the quickly developed global digital seismograph network has been providing high quality recordings of large earthquakes in global scale, based on which digital seismology has made great progress. Compared with large earthquakes, moderate and small sized shocks have more frequent occurrence, and comprise clues to geological tectonics and tectonic stress field in a region. Preceding and following a large earthquake, usually occur numbers of small events that im… 相似文献
11.
《地震学报(英文版)》1993,6(2):409-416
Making use of 75 earthquake data of China mainland and adjacent areas recorded by long period seismometers of 27 stations
of China and 3 stations of WWSSN and processed by match-filtering frequency-time analysis technique and grid dispersion inversion,
the authors obtain pure-path dispersion curves of Rayleigh surface wave in 147 grids in this paper.
The distribution characteristics of group velocity are as follows:the China mainland and its adjacent sea areas are divided
into two parts of east and west by South-North belt and are separated in blocks of south and north with boundaries of 44°–44°N,28°N
(in the west part) and 28°–32°N (in the east part), the first and third boundaries may extend eastward into sea regions, in
the west side of island arc and continental shelves, appears belt-form distribution of group velocity striping NE direction.
These distribution characteristics correspond to zonation of tectonic structure. In addition, the results also indicate that
the differences of group velocity dispersion curves exist between tectonic elements of next order. It is revealable for the
differences of group velocity among different tectonic elements until periodT = 113s (corresponding depth is about 170km).
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 32–38, 1993. 相似文献
12.
In this receiver function study, we investigate the structure of the crust beneath six seismic broadband stations close to
the Sunda Arc formed by subduction of the Indo-Australian under the Sunda plate. We apply three different methods to analyse
receiver functions at single stations. A recently developed algorithm determines absolute shear-wave velocities from observed
frequency-dependent apparent incidence angles of P waves. Using waveform inversion of receiver functions and a modified Zhu
and Kanamori algorithm, properties of discontinuities such as depth, velocity contrast, and sharpness are determined. The
combination of the methods leads to robust results. The approach is validated by synthetic tests. Stations located on Malaysia
show high-shear-wave velocities (V
S) near the surface in the range of 3.4–3.6 km s − 1 attributed to crystalline rocks and 3.6–4.0 km s − 1 in the lower crust. Upper and lower crust are clearly separated, the Moho is found at normal depths of 30–34 km where it
forms a sharp discontinuity at station KUM or a gradient at stations IPM and KOM. For stations close to the subduction zone
(BSI, GSI and PSI) complexity within the crust is high. Near the surface low V
S of 2.6–2.9 km s − 1 indicate sediment layers. High V
S of 4.2 km s − 1 are found at depth greater than 6 and 2 km at BSI and PSI, respectively. There, the Moho is located at 37 and 40 km depth.
At station GSI, situated closest to the trench, the subducting slab is imaged as a north-east dipping structure separated
from the sediment layer by a 10 km wide gradient in V
S between 10 and 20 km depth. Within the subducting slab V
S ≈ 4.7 km s − 1. At station BSI, the subducting slab is found at depth between 90 and 110 km dipping 20° ± 8° in approximately N 60° E. A
velocity increase in similar depth is indicated at station PSI, however no evidence for a dipping layer is found. 相似文献
13.
—A finite-source rupture model of the July 30, 1995, M w = 8.1 Antofagasta (Northern Chile) subduction earthquake is developed using body and surface waves that span periods from 20 to 290s. A long-period (150–290s) surface-wave spectral inversion technique is applied to estimate the average finite-fault source properties. Deconvolutions of broadband body waves using theoretical Green’s functions, and deconvolutions of broadband fundamental mode surface waves using empirical Green’s functions provided by a large aftershock, yield effective source time functions containing periods from 20 to 200s for many directivity parameters. The source time functions are used in an inverse radon transform to image a one-dimensional spatial model of the moment rate history. The event produced a predominantly unilateral southward rupture, yielding strong directivity effects on all seismic waves with periods less than a few hundred seconds. The aftershock information, spectral analysis, and moment rate distribution indicate a rupture length of 180–200km, with the largest slip concentrated in the first 120km, a rupture azimuth of 205°± 10° along the Chilean coastline, and a rupture duration of 60–68s with a corresponding average rupture velocity of 3.0–3.2km/s. The overall rupture character is quite smooth, accentuating the directivity effects and reducing the shaking intensity, however there are three regions with enhanced moment rate distributed along the rupture zone near the epicenter, 50 to 80km south of the epicenter, and 110 to 140km south of the epicenter. 相似文献
14.
The average annual values of the electric field and parameters of the solar wind and IMF from our time to 1868 have been estimated
based on the statistical relation between the aa index of geomagnetic activity and the interplanetary medium parameters. This estimation indicates that the relative variations
during the 20th century were observed in the electric field (25 ± 3%), the IMF vector component transverse with respect to
the velocity (16 ± 3%), and the solar wind plasma velocity (9 ± 1%, 37 ± 4 km/s). The modulus of the IMF vector radial component
increased by 9.0 ± 2.5% during this period. 相似文献
15.
The source parameters, such as moment tensor, focal mechanism, source time function (STF) and temporal-spatial rupture process,
were obtained for the January 26, 2001, India, M
S=7.8 earthquake by inverting waveform data of 27 GDSN stations with epicentral distances less than 90°. Firstly, combining
the moment tensor inversion, the spatial distribution of intensity, disaster and aftershocks and the orientation of the fault
where the earthquake lies, the strike, dip and rake of the seismogenic fault were determined to be 92°, 58° and 62°, respectively.
That is, this earthquake was a mainly thrust faulting with the strike of near west-east and the dipping direction to south.
The seismic moment released was 3.5×1020 Nm, accordingly, the moment magnitude M
W was calculated to be 7.6. And then, 27 P-STFs, 22 S-STFs and the averaged STFs of them were determined respectively using
the technique of spectra division in frequency domain and the synthetic seismogram as Green’s functions. The analysis of the
STFs suggested that the earthquake was a continuous event with the duration time of 19 s, starting rapidly and ending slowly.
Finally, the temporal-spatial distribution of the slip on the fault plane was imaged from the obtained P-STFs and S-STFs using
an time domain inversion technique. The maximum slip amplitude on the fault plane was about 7 m. The maximum stress drop was
30 MPa, and the average one over the whole rupture area was 7 MPa. The rupture area was about 85 km long in the strike direction
and about 60 km wide in the down-dip direction, which, equally, was 51 km deep in the depth direction. The rupture propagated
50 km eastwards and 35 km westwards. The main portion of the rupture area, which has the slip amplitude greater than 0.5 m,
was of the shape of an ellipse, its major axis oriented in the slip direction of the fault, which indicated that the rupture
propagation direction was in accordance with the fault slip direction. This phenomenon is popular for strike-slip faulting,
but rather rare for thrust faulting. The eastern portion of the rupture area above the initiation point was larger than the
western portion below the initiation point, which was indicative of the asymmetrical rupture. In other words, the rupturing
was kind of unilateral from west to east and from down to up. From the snapshots of the slip-rate variation with time and
space, the slip rate reached the largest at the 4th second, that was 0.2 m/s, and the rupture in this period occurred only
around the initiation point. At the 6th second, the rupture around the initiation point nearly stopped, and started moving
outwards. The velocity of the westward rupture was smaller than that of the eastward rupture. Such rupture behavior like a
circle mostly stopped near the 15th second. After the 16th second, only some patches of rupture distributed in the outer region.
From the snapshots of the slip variation with time and space, the rupture started at the initiation point and propagated outwards.
The main rupture on the area with the slip amplitude greater than 5 m extended unilaterally from west to east and from down
to up between the 6th and the 10th seconds, and the western segment extended a bit westwards and downwards between the 11th
and the 13th seconds. The whole process lasted about 19 s. The rupture velocity over the whole rupture process was estimated
to be 3.3 km/s.
Foundation item: 973 Project (G1998040705) from Ministry of Science and Technology, P. R. China, and the National Science Foundation of China
under grant No.49904004.
Contribution No. 02FE2026, Institute of Geophysics, China Seismological Bureau. 相似文献
16.
Hernando Tavera Efraín Fernández Isabel Bernal Yanet Antayhua Consuelo Agüero Henry Salas Simeón Rodríguez Luis Vilcapoma Yolanda Zamudio David Portugal Adolfo Inza Julia Carpio Freddy Ccallo Igor Valdivia 《Journal of Seismology》2006,10(2):171-195
The western border of South America is one of the most important seismogenic regions in the world. In this region the most damaging earthquake ever recorded occurred. In June 23rd, 2001, another very strong earthquake (Mw = 8.1–8.2) occurred and produced death and damages in the whole southern region of Peru. This earthquake was originated by a friction process between Nazca and South American plates and affected an area of about 300 km × 120 km defined by the distribution of more than 220 aftershocks recorded by a local seismic network that operated 20 days. The epicenter of the main shock was localized in the northwestern extremity of the aftershock area, which suggests that the rupture propagated towards the SE direction. The modeling of P-wave for teleseismic distances permitted to define a focal mechanism of reverse type with NW-SE oriented nodal planes and a possible fault plane moving beneath almost horizontally in NE direction. The source time function (STF) suggests a complex process of rupture during 85 sec with 2 successive sources. The second one of greater size, and located approximately 100–120 km toward the SE direction was estimated to have a rupture velocity of about 2 km/sec on a 28°-dipping plane to the SE (N135°). A second event happened 45 sec after the first one with an epicenter 130km farther to the SE and a complex STF. This event and the second source of the main shock caused a Tsunami with waves from 7 to 8 meters that propagated almost orthogonally to the coast line, by affecting mainly the Camaná area.Three of all the aftershocks presented magnitudes greater or equal to Mw = 6.6, two of them occurred in front of the cities of Ilo and Mollendo (June 26th and July 7th) with focal mechanisms similar to the main seismic event. The aftershock of July 5th shows a normal mechanism at a depth of 75 km, and is therefore most likely located within the subducting Nazca plate and not in the coupling. The aftershocks of June 26th (Mw = 6.6) and July 5th (Mw = 6.6) show simple short duration STF. The aftershock of July 7th (Mw = 7.5) with 27-second duration suggests a complex process of energy release with the possible occurrence of a secondary shock with lower focal depth and focal mechanism of inverse type with a great lateral component. Simple and composed focal mechanisms were elaborated for the aftershocks and all have similar characteristics to the main earthquake.The earthquake of June 23rd caused major damages in the whole southern Peru. The damage in towns of Arequipa, Moquegua allow to consider maximum intensities from 6 to 7 (MSK79). In Alto de la Alianza and Ciudad Nueva zones from Tacna, the maximum intensity was of 7− (MSK79). 相似文献
17.
Prantik Mandal R. K. Chadha N. Kumar I. P. Raju C. Satyamurty 《Pure and Applied Geophysics》2007,164(10):1963-1983
During the last six years, National Geophysical Research Institute, Hyderabad has established a semi-permanent seismological
network of 5–8 broadband seismographs and 10–20 accelerographs in the Kachchh seismic zone, Gujarat with a prime objective
to monitor the continued aftershock activity of the 2001 Mw 7.7 Bhuj mainshock. The reliable and accurate broadband data for the 8 October Mw 7.6 2005 Kashmir earthquake and its aftershocks from this network as well as Hyderabad Geoscope station enabled us to estimate
the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the Peninsular India.
Firstly, we measure Rayleigh-and Love-wave group velocity dispersion curves in the period range of 8 to 35 sec and invert
these curves to estimate the crustal and upper mantle structure below the western part of Peninsular India. Our best model
suggests a two-layered crust: The upper crust is 13.8 km thick with a shear velocity (Vs) of 3.2 km/s; the corresponding values
for the lower crust are 24.9 km and 3.7 km/sec. The shear velocity for the upper mantle is found to be 4.65 km/sec. Based
on this structure, we perform a moment tensor (MT) inversion of the bandpass (0.05–0.02 Hz) filtered seismograms of the Kashmir
earthquake. The best fit is obtained for a source located at a depth of 30 km, with a seismic moment, Mo, of 1.6 × 1027 dyne-cm, and a focal mechanism with strike 19.5°, dip 42°, and rake 167°. The long-period magnitude (MA ~ Mw) of this earthquake is estimated to be 7.31. An analysis of well-developed sPn and sSn regional crustal phases from the bandpassed
(0.02–0.25 Hz) seismograms of this earthquake at four stations in Kachchh suggests a focal depth of 30.8 km. 相似文献
18.
L. Matias N. A. Dias I. Morais D. Vales F. Carrilho J. Madeira J. L. Gaspar L. Senos A. B. Silveira 《Journal of Seismology》2007,11(3):275-298
The Faial earthquake (M
L 5.8) that occurred on the 9th of July, 1998, in the Azores region (north Atlantic), caused nine casualties and severe destruction
affecting more than 5,000 people. The main shock was located at sea, 10 km NE of the Faial Island, and triggered a seismic
sequence that lasted for several weeks and was characterized by an unusual high p-value of 1.40 for the modified Omori law. We present here the results of a joint inversion of hypocenters and 1D velocity
model performed on the data collected by the permanent network complemented with a temporary network installed shortly after
the occurrence of the main event. The 1D velocity model shows a heterogeneous upper crust, testified by the observed differences
in site effects at the stations, while the middle crust from ∼2.5 to 8 km in depth is quite homogeneous. The Moho is located
at a depth of about 12–13 km and the Vp/Vs ratio is found to be around 1.78. The events at depth are mainly concentrated in
the middle-lower crust (8–12 km), while their spatial distribution shows a main cluster, visible after relocation, SSE trending.
This direction of elongation is consistent with one of the fault planes (N151°E) of the centroid moment tensor (CMT) solution
for the main shock. The same plane is the preferred main shock fault plane inferred after a Coulomb failure function analysis
on the aftershock distribution. The main event relocation points to a focal depth shallower than 5 km. The aftershocks pattern
shows that several fault systems were reactivated by the stress perturbation induced by the main shock. Besides the two main
tectonic directions, trending WNW–ESE and NNW–SSE, observed in the tectonics of Faial, Pico, and S. Jorge, there is also evidence
of a new tectonic direction trending WSW–ENE. 相似文献
19.
In the region southeast of Okinawa, during May to July 2001, a cyclonic and an anticyclonic eddy were observed from combined measurements of hydrocasts, an upward-looking moored acoustic Doppler current profiler (MADCP), pressure-recording inverted echo sounders (PIESs), satellite altimetry, and a coastal tide gauge. The hydrographic data showed that the lowest/highest temperature (T) and salinity (S) anomalies from a 13-year mean for the same season were respectively -3.0/ 2.5℃ and -0.20/ 0.15 psu at 380/500 dbar for the cyclonic/anticyclonic eddies. From the PIES data, using a gravest empirical mode method, we estimated time-varying surface dynamic height (D) anomaly referred to 2000 dbar changing from -20 to 30 cm, and time-varying T and S anomalies at 500 dbar ranging through about ±2 ℃ and ±0.2 psu, respectively. The passage of the eddies caused variations of both satellite-measured sea surface height anomaly (SSHA) and tide-gauge-measured sea level anomaly to change from about –20 to 30 cm, consistent with the D anomaly from the PIESs. Bottom pressure sensors measured no variation related to these eddy activities, which indicated that the two eddies were dominated by baro-clinicity. Time series of SSHA map confirmed that the two eddies, originating from the North Pacific Subtropical Countercurrent region near 20°―30°N and 150°―160°E, traveled about 3000 km for about 18 months with mean westward propagation speed of about 6 cm/s, before arriving at the region southeast of Okinawa Island. 相似文献
20.
基于一维单侧有限移动震源模式,根据地震波传播过程中的多普勒效应,分别利用P波和S波拐角频率的方位变化,反演2012年7月20日江苏高邮、宝应交界MS4.9地震的发震断层面参数。P波和S波拐角频率的反演结果一致显示:本次地震的断层面破裂方向为232°左右,破裂面呈NE-SW向;地震马赫数v/c为0.2左右,平均破裂速度小于S波速度,破裂长度较短,为0.2~0.3km左右。破裂面方位与震源机制解、宏观烈度调查和余震精定位的研究结果具有一致性,结合震区周边的地质构造背景,分析认为滁河断裂很可能是高邮、宝应交界MS4.9地震的发震构造。 相似文献