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1.
We study eight tsunamigenic earthquakes of 1992–1994 with data from single near-field 3-component long-period stations. The analysis is made from the standpoint of tsunami warning by an automatic process which estimates the epicentral location and the seismic moment through the variable-period mantle magnitudeM
m
. Simulations of early warning based on the real-time computation of the seismic moment are also tested with this system, which would give a justified warning in each region of tsunami potentiality. By exploiting the dependence of moment rate release with frequency, the system has the capability of recognizing both tsunami earthquakes such as the 1992 Nicaragua and 1994 Java events, as well as instances of the opposite case of low-frequency deficiency, interpreted as indicating a deeper than normal source (1993 Guam event). We report both the results of delayed-time processing of the near-field stations, and the actual real-time warnings at PPT, which confirm the former. 相似文献
2.
We conducted moment tensor inversion and studied source rupture process for M
S=7.9 earthquake occurred in the border area of China, Russia and Mongolia on September 27 2003, by using digital teleseismic
P-wave seismograms recorded by long-period seismograph stations of the global seismic network. Considering the aftershock
distribution and the tectonic settings around the epicentral area, we propose that the M
S=7.9 earthquake occurred on a fault plane with the strike of 127°, the dip of 79° and the rake of 171°. The rupture process
inversion result of M
S=7.9 earthquake shows that the total rupture duration is about 37 s, the scalar moment tensor is M
0=0.97×1020 N·m. Rupture mainly occurred on the shallow area with 110 km long and 30 km wide, the location in which the rupture initiated
is not where the main rupture took place, and the area with slip greater than 0.5 m basically lies within 35 km deep middle-crust
under the earth surface. The maximum static slip is 3.6 m. There are two distinct areas with slip larger than 2.0 m. We noticed
that when the rupture propagated towards northwest and closed to the area around the M
S=7.3 hypocenter, the slip decreased rapidly, which may indicate that the rupture process was stopped by barriers. The consistence
of spatial distribution of slip on the fault plane with the distribution of aftershocks also supports that the rupture is
a heterogeneous process owing to the presence of barriers. 相似文献
3.
Rengin Gök Lawrence Hutchings Kevin Mayeda Doğan Kalafat 《Pure and Applied Geophysics》2009,166(4):547-566
We develop a data set of aftershock recordings of the 1999, M = 7.4 Izmit and M = 7.2 Duzce (Turkey) earthquakes to study
their source parameters. We combined seismograms from 44 stations maintained by several sources (organizations) to obtain
a unified data set of events (2.1 ≤ Mw ≤ 5.5). We calculate source parameters of these small earthquakes by two methods that use different techniques to address
the difficulty in obtaining source spectra for small earthquakes subject to interference from site response. One method (program
NetMoment (NM), Hutchings, 2004) uses spectra of direct S waves in a simultaneous inversion of local high-frequency network data to estimate seismic
moment, source corner frequency (fc), site attenuation (k) and whole-path Q. This approach takes advantage of the source commonality in all recordings for a particular earthquake
by fitting a common Brune source spectrum to the data with a and individual k. The second approach (Mayeda et al., 2003) uses the coda method (CM) to obtain “nonmodel-based” source spectra and moment estimates from selected broadband
recording sites. We found that both methods do well for events that allow the comparison with seismic moment estimates derived
from waveform modeling. Also, source spectra obtained from the two methods are very closely matched for most of the events
they have in common. We use an F test to examine the trade-off between k and fc picks identified by the direct S-wave method. About half of the events could be constrained to have less than a 50% average
uncertainty in fc and k. We used these source spectra solutions to calculate energy and apparent stress and compare these to estimates from the selected
“good quality” source spectra from CM. Both studies have values mutually consistent and show a similar increase in apparent
stress with increasing moment. This result has added merit due to the independent approaches to calculate apparent stress.
We conclude that both methods are at least partially validated by our study, and they both have usefulness for different circumstances
of recording local small earthquakes. CM would work well in studies for which there is a broad magnitude range of events and
NM works well for local events recorded by band-limited recorders. 相似文献
4.
Marian Ivan 《Journal of Seismology》2007,11(1):73-85
The seismic attenuation in the Vrancea region (Romania) is investigated from teleseismic recordings of P and pP waves during
the four major, intermediate-depth Romanian events that occurred since the onset of digital instrumentation. Most stations
are located in Canada and in the United States, being equipped with a variety of sensors, especially short-period ones. The
amplitude spectral ratio method is used, assuming no frequency dependence of the Q
P factor in the range 0.2–2 Hz. No apparent correlation between the derived attenuation value and the type of recording sensor
is observed. Lateral variations of the attenuation are obtained, with a very low Q
P area (values down to 33) located in the northwestern part of the Vrancea seismogenic volume. For the stations with different
azimuth angles in relation to the epicentral area, Q
P values routinely exceed 200. Most likely, the low attenuation values are related to an upwelling mantle material located
immediately beneath the crust, but limited in depth to at least 100 km. 相似文献
5.
We conducted moment tensor inversion and studied source rupture process for M S=7.9 earthquake occurred in the border area of China, Russia and Mongolia on September 27 2003, by using digital teleseismic P-wave seismograms recorded by long-period seismograph stations of the global seismic network. Considering the aftershock distribution and the tectonic settings around the epicentral area, we propose that the M S=7.9 earthquake occurred on a fault plane with the strike of 127°, the dip of 79° and the rake of 171°. The rupture process inversion result of M S=7.9 earthquake shows that the total rupture duration is about 37 s, the scalar moment tensor is M 0=0.97×1020 N·m. Rupture mainly occurred on the shallow area with 110 km long and 30 km wide, the location in which the rupture initiated is not where the main rupture took place, and the area with slip greater than 0.5 m basically lies within 35 km deep middle-crust under the earth surface. The maximum static slip is 3.6 m. There are two distinct areas with slip larger than 2.0 m. We noticed that when the rupture propagated towards northwest and closed to the area around the M S=7.3 hypocenter, the slip decreased rapidly, which may indicate that the rupture process was stopped by barriers. The consistence of spatial distribution of slip on the fault plane with the distribution of aftershocks also supports that the rupture is a heterogeneous process owing to the presence of barriers. 相似文献
6.
An earthquake ofM
S=6.9 occurred at the Gonghe, Qinghai Province, China on April 26, 1990. Three larger aftershocks took place at the same region,M
S=5.5 on May 7, 1990,M
S=6.0 on Jan. 3, 1994 andM
S=5.7 on Feb. 16, 1994. The long-period recordings of the main shock from China Digital Seismograph Network (CD-SN) are deconvolved
for the source time functions by the correspondent recordings of the three aftershocks as empirical Green’s functions (EGFs).
No matter which aftershock is taken as EGF, the relative source time functions (RSTFs) obtained are nearly identical. The
RSTFs suggest theM
S=6.9 event consists of at least two subevents with approximately equal size whose occurrence times are about 30 s apart, the
first one has a duration of 12 s and a rise time of about 5 s, and the second one has a duration of 17 s and a rise time of
about 8 s. Comparing the RSTFs obtained from P- and SH-phases respectively, we notice that those from SH-phases are a slightly
more complex than those from P-phases, implying other finer subevents exist during the process of the main shock. It is interesting
that the results from the EGF deconvolution of long-period wavform data are in good agreement with the results from the moment
tensor inversion and from the EGF deconvolution of broadband waveform data. Additionally, the two larger aftershocks are deconvolved
for their RSTFs. The deconvolution results show that the processes of theM
S=6.0 event on Jan. 3, 1994 and theM
S=5.7 event on Feb. 16, 1994 are quite simple, both RSTFs are single impulses.
The RSTFs of theM
S=6.9 main shock obtained from different stations are noticed to be azimuthally dependent, whose shapes are a slightly different
with different stations. However, the RSTFs of the two smaller aftershocks are not azimuthally dependent. The integrations
of RSTFs over the processes are quite close to each other, i. e., the scalar seismic moments estimated from different stations
are in good agreement.
Finally the scalar seismic moments of the three aftershocks are compared. The relative scalar seismic moment of the three
aftershocks deduced from the relative scalar seismic moments of theM
S=6.9 main shock are very close to those inverted directly from the EGF deconvolution. The relative scalar seismic moment of
theM
S=6.9 main shock calculated using the three aftershocks as EGF are 22 (theM
S=6.0 aftershock being EGF), 26 (theM
S=5.7 aftershock being EGF) and 66 (theM
S=5.5 aftershock being EGF), respectively. Deducing from those results, the relative scalar sesimic moments of theM
S=6.0 to theM
S=5.7 events, theM
S=6.0 to theM
S=5.5 events and theM
S=5.7 to theM
S=5.5 events are 1.18, 3.00 and 2.54, respectively. The correspondent relative scalar seismic moments calculated directly from
the waveform recordings are 1.15, 3.43, and 3.05.
Contribution No. 96B0007, Institute of Geophysics, SSB, China. 相似文献
7.
On 22 September 2002, the largest UK earthquake (mb4.3) of the last 10 years occurred near the town of Dudley in the West Midlands. Here we determine the earthquake focal mechanism and depth using data from stations at regional and teleseismic distances. Short-period teleseismic seismograms are interpreted in terms of P and surface reflections pP and sP. This analysis suggests that the source depth is deeper than the 9.7 km initially determined by the British Geological Survey (BGS). The relative amplitude method is applied to four teleseismic seismograms to support our interpretation of the surface reflections, and constrain the focal mechanism. Our preferred focal mechanism, a near vertical strike-slip with s = 94°, = 88° and = –179°, is in reasonable agreement with a moment tensor determined by the Swiss Seismological Service. Synthetic regional surface wave seismograms match the observed seismograms for a model focal depth of 19.5 (±3.0) km and scalar moment, M0, of 3.2 × 1015 N m. Our results emphasize that due to the well-known trade-off between depth and M0 from inversions of long period (0.02–0.1 Hz) surface waves, it is preferable to combine long- and short-period data to constrain reliably the depth and hence estimate M0. Our focal mechanism and depth are further validated by generating short-period synthetic seismograms that match the observations. 相似文献
8.
Mihnea Corneliu Oncescu 《Pure and Applied Geophysics》1986,124(4-5):931-940
The method of relative seismic moment tensor determination proposed byStrelitz (1980) is extended a) from an interactive time domain analysis to an automated frequency domain procedure, and b) from an analysis of subevents of complex deep-focus earthquakes to the study of individual source mechanism of small events recorded at few stations.The method was applied to the recovery of seismic moment tensor components of 95 intermediate depth earthquakes withM
L=2.6–4.9 from the Vrancea region, Romania. The main feature of the obtained fault plane solutions is the horizontality ofP axes and the nonhorizontal orienaation ofT axes (inverse faulting). Those events with high fracture energy per unit area of the fault can be grouped unambiguously into three depth intervals: 102–106 km, 124–135 km and 141–152 km. Moreover, their fault plane solutions are similar to ones of all strong and most moderate events from this region and the last two damaging earthquakes (November 10, 1940 withM
W=7.8 and March 4 1977 withM
W=7.5) occurred within the third and first depth interval, respectively. This suggests a possible correlation at these depths between fresh fracture of rocks and the occurrence of strong earthquakes. 相似文献
9.
Source Characteristics of the 12 November 1996 Mw 7.7 Peru Subduction Zone Earthquake 总被引：1，自引：0，他引：1
—The 12 November 1996 M w 7.7 Peru subduction zone earthquake occurred off the coast of southern Peru, near the intersection of the South American trench and the highest topographical point of the subducting Nazca Ridge. We model the broadband teleseismic P-waveforms from stations in the Global Seismic Network to constrain the source characteristics of this subduction zone earthquake. We have analyzed the vertical component P-waves for this earthquake to constrain the depth, source complexity, seismic moment and rupture characteristics. The seismic moment determined from the nondiffracted P-waves is 3–5 × 1020 N·m, corresponding to a moment magnitude M w of 7.6–7.7. The source time function for the 1996 Peru event has three pulses of seismic moment release with a total duration of approximately 45–50 seconds. The largest moment release occurs at approximately 35–40 seconds and is located ～90km southeast of the rupture initiation. Approximately 70% of the seismic moment was released in the third pulse.¶We find that the 1996 event reruptured part of the rupture area of the previous event in 1942. The location of the 1996 earthquake corresponds to a region along the Peru coast with the highest uplift rates of marine terraces. This suggests that the uplift may be due to repeated earthquakes such as the 1996 and 1942 events. 相似文献
10.
On July 25, 1969, anM
s
5.9 earthquake shook the Kwangtung Province near Yangjiang, China. Casualties and extensive damage were reported in the epicentral area. The Yangjiang earthquake occurred within the passive margin located along China's southeast coast. This stable continental setting is seismically one of the most quiet regions of China; historic records indicate this earthquake to have been the first devastating one in the area. A remarkable feature of this earthquake sequence is that its foreshocks and aftershocks are relatively small in terms of number and magnitude despite the relatively large main shock.Waveforms of long-and short-period teleseismicP and long-period teleseismicSH waves have been modeled to estimate the source parameters for this earthquake. The focal mechanism determined is predominately strike-slip with a small normal component (strike=263°, dip=79°, rake=194°) and is in good agreement with observations in the epicentral area regarding dislocation direction of fissures, distribution of aftershocks, and isoseismals. The average seismic moment is 5.15×1024 dyne-cm and the focal depth is estimated to be 9 km. The earthquake is characterized by a rather short source-time function and a high stress drop of approximately 380 bars. The observed pattern of the foreshock-main shock-aftershock sequence is interpreted in terms of the large stress drop associated with the main shock and the material properties at and near the source. TheP-axis orientation lies roughly NW-SE and is consistent with the maximum compressive stress observed along the coast of southeast China. This stress orientation is consistent with the NW subducting Philippine Sea plate and the SE ward push from central China due to the convergence between Indian and Eurasian subcontinents. 相似文献
11.
The dense broadband seismic network provides more high-quality waveform that is helpful to improve constraint focal depth of shallow earthquake. Many shallow earthquakes occurring in sediment were regarded as induced events. In Sichuan basin, gas industry and salt mining are dependent on fluid injection technique that triggers microseismicity. We adopted waveform inversion method with regional records to obtain focal mechanism of an M s4.8 earthquake at Changning. The result suggested that the Changning earthquake occurred at a ESE thrust fault, and its focal depth was about 3 km. The depth phases including teleseismic pP phase and regional sPL phase shows that the focal depth is about 2 km. The strong, short-period surface wave suggests that this event is a very shallow earthquake. The amplitude ratio between Rayleigh wave and direct S wave was also used to estimate the source depth of the mainshock. The focal depth (2–4 km) is far less than the depth of the sedimentary layer thickness (6–8 km) in epicentral region. It is close to the depth of fluid injection of salt mining, which may imply that this event was triggered by the industrial activity. 相似文献
12.
According to earthquake catalog records of Fujian Seismic Network, the T now method and the four-station continuous location method put forward by Jin Xing are inspected by using P-wave arrival information of the first four stations in each earthquake. It shows that the four-station continuous location method can locate more seismic events than the T now method. By analyzing the results, it is concluded that the reason for this is that the T now method makes use of information from stations without being triggered, while some stations failed to be reflected in earthquake catalog because of discontinuous records or unclear records of seismic phases. For seismic events whose location results can be given, there is no obvious difference in location results of the two methods and positioning deviation of most seismic events is also not significant. For earthquakes outside the network, the positioning deviation may amplify as the epicentral distance enlarges, which may relate to the situation that the seismic stations are centered on one side of epicenter and the opening angle between seismic stations used for location and epicenter is small. 相似文献
13.
We have determined the rupture history of the March 28, 1964, Prince Williams Sound earthquake (M
w=9.2) from long-period WWSSNP-wave seismograms. Source time functions determined from the long-periodP waves indicate two major pulses of moment release. The first and largest moment pulse has a duration of approximately 100 seconds with a relatively smooth onset which reaches a peak moment release rate at about 75 seconds into the rupture. The second smaller pulse of moment release starts at approximately 160 seconds after the origin time and has a duration of roughly 40 seconds. Because of the large size of this event and thus a deficiency of on-scale, digitizableP-wave seismograms, it is impossible to uniquely invert for the location of moment release. However, if we assume a rupture direction based on the aftershock distribution and the results of surface wave directivity studies we are able to locate the spatial distribution of moment along the length of the fault. The first moment pulse most likely initiated near the epicenter at the northeastern down-dip edge of the aftershock area and then spread over the fault surface in a semi-circular fashion until the full width of the fault was activated. The rupture then extended toward the southwest approximately 300 km (Ruff andKanamori, 1983). The second moment pulse was located in the vicinity of Kodiak Island, starting at 500 km southwest of the epicenter and extending to about 600 km. Although the aftershock area extends southwest past the second moment pulse by at least 100 km, the moment release remained low. We interpret the 1964 Prince William Sound earthquake as a multiple asperity rupture with a very large dominant asperity in the epicentral region and a second major, but smaller, asperity in the Kodiak Island region.The zone that ruptured in the 1964 earthquake is segmented into two regions corresponding to the two regions of concentrated moment release. Historical earthquake data suggest that these segments behaved independently during previous events. The Kodiak Island region appears to rupture more frequently with previous events occurring in 1900, 1854, 1844, and 1792. In contrast, the Prince William Sound region has much longer recurrence intervals on the order of 400–1000 years. 相似文献
14.
Spectral parameters have been estimated for 214 Petatlan aftershocks recorded at stations between Petatlan and Mexico City and between Petatlan and Acapulco. The spectral parameters were used to obtain empirical relations for the estimation of seismic moment from coda length and fromM
L
. Stress drops, using Brune's model, were calculated for these aftershocks. Six events with large stress drop are located within a previously suggested asperity, and seven more suggest a boundary zone at the intersection of the Petatlan and Zihuatanejo aftershock rupture volumes. Stress drops increase with increasing seismic moment up to 1020 dyne-cm but appear to be constant at greater moment values. The peak horizontal velocity times distance of aftershocks recorded near the coast and between the coast and Mexico City (30 to 270 km away), scales linearly with seismic moment, and predicts well the peak horizontal values of large (M
s
7.0) coastal thrust events recorded on rock sites at Mexico City. Peak horizontal velocity is a straightforward measurement, thus this relation allows us to evaluate expected ground motion between the Pacific coast and Mexico City from the seismic moment of subduction related earthquakes along the coast. 相似文献
15.
The caustic of SKP is found at an epicentral distance ΔC = 129.5° for surface foci and at ΔC = 128.9° for foci at 400 km depth, by means of amplitude-distance graphs based upon short-period time-domain measurements. These results are essentially confirmed by long-period time-domain measurements of SKP as well as by frequency-domain studies, even though the spectra are less accurate for such determinations. The average period of SKP is from short-period records, significantly different from the corresponding PKP-period of 1.00 ± 0.31 sec. Likewise, the long-period averages of SKP = 10.8 ± 4.5 sec and of PKP = 7.7 ± 3.0 sec are significantly different from each other. A travel-time table of SKP1 is deduced, covering the epicentral distance range of 130–143° and the focal depth range of 100–700 km. All results are based on measurements on seismograms of the Swedish network of stations, deriving almost exclusively from earthquakes in the southwest Pacific area. 相似文献
16.
The Alaska Tsunami Warning Center has the responsibility of providing timely tsunami warning services for Alaska and the west coasts of Canada and the United States. Recently, the ATWC implemented a new microcomputer system which is used for both automatic and interactive earthquake processing, and for disseminating critical information to the Tsunami Warning System recipients.Real-time seismic wave form data from 23 short-period and 9 long-period sites in Alaska, the lower 48 States, and Hawaii, are continually computer-monitored for the occurrence of an earthquake. Once detected from the short-period wave form data, pre- and post-earthquake data are displayed on a graphics terminal along with an indicator to identify the time of the onset of theP waves (P-picks). TheP-picks can easily be changed during or after data collection via a mouse. Magnitudes (M
b
,M
l
,M
B
,M
S
) are automatically computed from appropriate short- and long-period wave form data concurrently with the above processing. A second graphics terminal displays cycle-by-cycle long-period wave form data that was used to compute an earthquake'sM
B
andM
S
magnitudes.An earthquake's parametric data and other information are available and printed within tens of seconds after theP wave arrivals are recorded at the first 5 sites, then 7 sites, 9 sites, and a final parametric computation using all collected data. Three video display monitors are used for displaying the parameters, procedural aids, and a map showing the epicenter. Additionally, selected event parameters are immediately transmitted by VHF radio to alphanumeric beepers which are carried by standby duty personnel during those times that the Center is not manned.Using a dedicated video display terminal and printer, the interactive system can use data and parameters resulting from the automatic processes for concurrent parameter recomputations; perform additional computations; disseminate critical information; and generate procedural aids for duty geophysicists to facilitate an earthquake/tsunami investigation. 相似文献
17.
—On December 22nd, 1999 an earthquake of Magnitude Mw : 5.7 occurred at Ain Temouchent (northwest Algeria). This moderate seismic event was located in a region characterized by a low seismic activity where few historical events have been observed. The earthquake, with a maximum intensity of VII (MSK scale), caused serious damages to the Ain Temouchent city and its surroundings. In the epicentral area, 25 people died and about 25,000 people were made homeless. Some minor breaks have been observed in several areas in the field. They were mainly related to minor collapses in the landscape or in volcanic cavities. The focal mechanism has been studied by using broadband data at regional and teleseismic distances, and different methods. The fault-plane solution has been estimated from first motions of P wave. Depth and source time function have been estimated from the modeling of body waveforms. Scalar seismic moment and source dimension have been obtained from spectral analysis. Results show thrust motion, with a horizontal pressure axis oriented in a NW-SE direction, a depth of 4 km and a simple source time function with time duration of 5 s. Scalar seismic moment estimated from waveform modeling is 4.7 × 1017 Nm, and spectral analysis gives a value of 1.7 × 1017 Nm and a source radius of 7.5 km. 相似文献
18.
19.
—The development of the digital seismic network in the Azores Archipelago during recent years made it possible to obtain the amplitudes (waveform) of recorded motion in a large set of stations. With this new data, maximum amplitudes of the Wood Anderson seismograph are computed, for each station/component, which, together with epicentral distances, allows for the estimation of local magnitude M
L
. We used data recorded in 8 digital permanent three-component stations, with inter-stations distances up to 300 km, in the period June 1998 – June 2000, corresponding to a set of 1315 events with magnitude (M
L
or M
D
) 2<M<5.8 and epicenters located in the Azores region, to estimate the coefficients of the equation to compute M
L
, as well as to determine the corrections to be applied to each station. The new set of parameters, formed by attenuation coefficients and station corrections, were introduced in the calculations of the M
L
, leading to smaller dispersions in the analyzed dataset. We also conclude that the attenuation in the first 150 km is similar to the California values, although higher for longer distances. 相似文献
20.
Calibration of the Regional Crustal Waveguide and the Retrieval of Source Parameters Using Waveform Modeling 总被引：5，自引：0，他引：5
v--vRegional crustal waveguide calibration is essential to the retrieval of source parameters and the location of smaller (M < 4.8) seismic events. This path calibration of regional seismic phases is strongly dependent on the accuracy of hypocentral locations of calibration (or master) events. This information can be difficult to obtain, especially for smaller events. Generally, explosion or quarry blast generated travel-time data with known locations and origin times are useful for developing the path calibration parameters, but in many regions such data sets are scanty or do not exist. We present a method which is useful for regional path calibration independent of such data, i.e. with earthquakes, which is applicable for events down to Mw = 4 and which has successfully been applied in India, central Asia, western Mediterranean, North Africa, Tibet and the former Soviet Union. These studies suggest that reliably determining depth is essential to establishing accurate epicentral location and origin time for events. We find that the error in source depth does not necessarily trade-off only with the origin time for events with poor azimuthal coverage, but with the horizontal location as well, thus resulting in poor epicentral locations. For example, hypocenters for some events in central Asia were found to move from their fixed-depth locations by about 20 km. Such errors in location and depth will propagate into path calibration parameters, particularly with respect to travel times. The modeling of teleseismic depth phases (pP, sP) yields accurate depths for earthquakes down to magnitude Mw = 4.7. This Mw threshold can be lowered to four if regional seismograms are used in conjunction with a calibrated velocity structure model to determine depth, with the relative amplitude of the Pnl waves to the surface waves and the interaction of regional sPmP and pPmP phases being good indicators of event depths. We also found that for deep events a seismic phase which follows an S-wave path to the surface and becomes critical, developing a head wave by S to P conversion is also indicative of depth. The detailed characteristic of this phase is controlled by the crustal waveguide. The key to calibrating regionalized crustal velocity structure is to determine depths for a set of master events by applying the above methods and then by modeling characteristic features that are recorded on the regional waveforms. The regionalization scheme can also incorporate mixed-path crustal waveguide models for cases in which seismic waves traverse two or more distinctly different crustal structures. We also demonstrate that once depths are established, we need only two-stations travel-time data to obtain reliable epicentral locations using a new adaptive grid-search technique which yields locations similar to those determined using travel-time data from local seismic networks with better azimuthal coverage. 相似文献