Contribution of seismic tomography in moment-tensor inversions using teleseismic surface-wave spectra

1997 ◽  
Vol 87 (1) ◽  
pp. 114-122
Author(s):  
Hugues Dufumier ◽  
Jeannot Trampert
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Moment Tensor ◽  
Frequency Filtering ◽  
Multiple Frequency ◽  
Moment Tensors ◽  
Long Period ◽  
Short Period ◽  
Earth Models ◽  
Filtering Techniques

Abstract The knowledge of lateral heterogeneities is crucial for path corrections in moment tensor inversions using surface waves. After some attempts to use regionalized Earth models for very long-period surface-wave moment-tensor inversions, recent tomographic Earth models offer the possibility to make short-period path corrections and therefore retrieve more reliable moment tensors for teleseismic earthquakes. First we try to evaluate the precision required for path corrections in comparison with source effects. Some selected Earth models are tested to evaluate how their results compare to those using multiple-frequency filtering techniques. Some real cases illustrate the sensitivity of moment-tensor solutions to the different path corrections, and it appears clearly that regionalized Earth models and tomographic models deduced from long-period data alone (greater than 150 sec) cannot lead to trustworthy broadband moment-tensor inversions. Recent tomographic models using phase velocities at much shorter periods (40 to 200 sec) offer a precision comparable to that of the multiple-frequency filtering technique. Both methods lead to acceptable source mechanisms, using a small number of stations, in more than two cases out of three. The use of recent global tomographic models based upon shorter-period surface waves might thus be a useful alternative to heavy multiple-frequency filtering techniques to automate source studies, especially for rapid determinations using a small number of stations.

Large Explosions at Sea

1971 ◽  
Vol 8 (2) ◽  
pp. 243-247
Author(s):  
Goetz G. R. Buchbinder
Keyword(s):  
Surface Wave ◽  
Continental Shelf ◽  
Surface Waves ◽  
Small Amplitude ◽  
Body Wave ◽  
Surface Wave Magnitude ◽  
Underwater Explosions ◽  
Long Period ◽  
Short Period ◽  
The Difference

Two large unannounced events occurred at sea in aseismic areas in the Atlantic. Comparison of these with the announced event Chase III shows them to be explosions.Large explosions at sea may be recognized by the relatively small amplitude of long period surface waves with periods up to 10 s. Energy of longer periods is absent for events mb ≤ 5.5. The surface wave magnitudes for the events are at least 1.5 smaller at 10 s than those of underground explosions of equal mb, at 20 s they are at least 0.9 smaller. At longer periods the difference between body wave and surface wave magnitude is larger than 0.9 but larger explosions are needed to determine the separation. Underwater explosions on or near the continental shelf are very efficient in the generation of higher mode short period waves.

scholarly journals Processing The Ground Motion Signal Recording Using Correction Instrument Method

Faktor Exacta ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 55
Author(s):  
Erna Kusuma Wati
Keyword(s):  
Surface Wave ◽  
Receiver Function ◽  
Moment Tensor ◽  
Theoretical Data ◽  
Wave Dispersion ◽  
Correction Method ◽  
Filter Method ◽  
Moment Tensors ◽  
Motion Signal ◽  
Short Period

<em>The instrument correction method is a way to eliminate interference with the signal from the recording instrument response. Signal processing by the instrument correction method using the inverse filter method created using the MATLAB program. In this research using Honshu earthquake data, Japan with Mw 7.4 (dated September 5, 2004) recorded by the MERAMEX seismometer type L4C-3D type short seismometer and Japan Tohoku-Oki earthquake with a strength of Mw 9.0 (March 11, 2011) the data from four seismic stations in Padang, West Sumatra with a DS-4A type short-period seismometer. From the research known, the signal can clearly show the phase of the P and S waves. This can help to determine the parameters of the hypocenter, receiver function, moment tensors, studies of</em> <em>.  The surface wave phase can be reconstructed well. This is very useful for studies using surface wave data, moment tensor solutions, seismic wave dispersion studies. Based on the amplitude of the instrument correction results compared with theoretical data, the gain or amplification </em> <strong><em>.</em></strong>

Effects of centroid location on determination of earthquake mechanisms using long-period surface waves

1990 ◽  
Vol 80 (5) ◽  
pp. 1205-1231
Author(s):  
Jiajun Zhang ◽  
Thorne Lay
Keyword(s):  
Surface Wave ◽  
Rayleigh Waves ◽  
Body Wave ◽  
Moment Tensor ◽  
Source Location ◽  
P Wave ◽  
Nodal Plane ◽  
Wave Source ◽  
Long Period

Abstract Determination of shallow earthquake source mechanisms by inversion of long-period (150 to 300 sec) Rayleigh waves requires epicentral locations with greater accuracy than that provided by routine source locations of the National Earthquake Information Center (NEIC) and International Seismological Centre (ISC). The effects of epicentral mislocation on such inversions are examined using synthetic calculations as well as actual data for three large Mexican earthquakes. For Rayleigh waves of 150-sec period, an epicentral mislocation of 30 km introduces observed source spectra phase errors of 0.6 radian for stations at opposing azimuths along the source mislocation vector. This is larger than the 0.5-radian azimuthal variation of the phase spectra at the same period for a thrust fault with 15° dip and 24-km depth. The typical landward mislocation of routinely determined epicenters of shallow subduction zone earthquakes causes source moment tensor inversions of long-period Rayleigh waves to predict larger fault dip than indicated by teleseismic P-wave first-motion data. For dip-slip earthquakes, inversions of long-period Rayleigh waves that use an erroneous source location in the down-dip or along-strike directions of a nodal plane, overestimate the strike, dip, and slip of that nodal plane. Inversions of strike-slip earthquakes that utilize an erroneous location along the strike of a nodal plane overestimate the slip of that nodal plane, causing the second nodal plane to dip incorrectly in the direction opposite to the mislocation vector. The effects of epicentral mislocation for earthquakes with 45° dip-slip fault mechanisms are more severe than for events with other fault mechanisms. Existing earth model propagation corrections do not appear to be sufficiently accurate to routinely determine the optimal surface-wave source location without constraints from body-wave information, unless extensive direct path (R1) data are available or empirical path calibrations are performed. However, independent surface-wave and body-wave solutions can be remarkably consistent when the effects of epicentral mislocation are accounted for. This will allow simultaneous unconstrained body-wave and surface-wave inversions to be performed despite the well known difficulties of extracting the complete moment tensor of shallow sources from fundamental modes.

LONG‐PERIOD SIGNAL PROCESSING RESULTS FOR THE LARGE APERTURE SEISMIC ARRAY

Geophysics ◽  
1969 ◽  
Vol 34 (3) ◽  
pp. 305-329 ◽  
Author(s):  
J. Capon ◽  
R. J. Greenfield ◽  
R. T. Lacoss
Keyword(s):  
Signal Processing ◽  
Surface Wave ◽  
Maximum Likelihood ◽  
Surface Waves ◽  
Body Wave ◽  
Seismic Array ◽  
Seismic Events ◽  
Long Period ◽  
Large Aperture ◽  
Period Data

The results of a series of off‐line signal processing experiments are presented for long‐period data obtained from the Large Aperture Seismic Array (LASA) located in eastern Montana. The signal‐to‐noise ratio gains obtained with maximum‐likelihood processing, as well as other simpler forms of processing, are presented for body‐wave as well as surface‐wave phases. A discussion of the frequency‐wavenumber characteristics of the noise which led to these results is also given. On the basis of these experiments, several recommendations are made concerning optimum long‐period array configurations and on‐line or off‐line processing methods. The usefulness of maximum‐likelihood processing in suppressing an interfering teleseism is demonstrated. An experiment is given in which maximum‐likelihood processing achieved about 20 db suppression of an interfering teleseism, while simpler forms of processing such as beam‐forming obtained about 11 db. The matched filtering of surface waves using chirp waveforms is shown to be highly effective. A useful discriminant for distinguishing between natural seismic events and underground nuclear explosions, using both the long‐period and short‐period data, was found to be the relationship between the surface‐wave and body‐wave magnitudes. Measurements of this discriminant made on events from four tectonic regions of the earth are presented. It is shown that 60 and 100 percent detectability of surface waves for natural seismic events from the Central Asian‐Kurile Islands‐Kamchatka region occurs at about LASA body‐wave magnitudes 4.5 and 4.9, respectively.

GULF COAST SURFACE WAVES

Geophysics ◽  
1953 ◽  
Vol 18 (1) ◽  
pp. 41-53 ◽  
Author(s):  
Lynn G. Howell ◽  
E. F. Neuenschwander ◽  
A. L. Pierson
Keyword(s):  
Rayleigh Wave ◽  
Surface Waves ◽  
Velocity Dispersion ◽  
Gulf Coast ◽  
Group Velocity Dispersion ◽  
Vertical Strain ◽  
Long Period ◽  
Short Period ◽  
Component Velocity ◽  
Wave Trains

Surface wave recordings were made with the following: a three‐component velocity seismometer, a long‐period displacement seismometer, six dynamic seismometers, an air‐actuated condenser microphone, and a vertical strain seismometer. Wave trains were recorded similar to those obtained by B. F. Howell in California. We have divided the surface waves into two trains instead of three. The early train seems to have properties of the M‐2 wave of Sezawa; the late train seems to be a Rayleigh wave. An air‐coupled wave is shown to be associated with the M‐2 wave. In the group velocity dispersion curve of the Rayleigh wave, the short‐period branch was found as predicted by theory as well as the usually observed long‐period branch. By making certain assumptions, the thickness of the top layer appears to be about 50 feet according to the theoretical curves of Kanai.

The October 6, 1974 Acapulco earthquake: An example of the importance of short-period surface waves in strong ground motion

1978 ◽  
Vol 68 (6) ◽  
pp. 1663-1677
Author(s):  
Stephen H. Hartzell ◽  
James N. Brune ◽  
Jorge Prince
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Epicentral Distance ◽  
Source Region ◽  
Crystalline Rock ◽  
Body Waves ◽  
Wave Number ◽  
Source Depth ◽  
Moment Estimate ◽  
Short Period

abstract The Acapulco earthquake of October 6, 1974 (mb = 5.0, Ms = 4.75) resulted in 0.5 g accelerations in Acapulco at an epicentral distance of about 35 km. Extrapolation of the peak acceleration to the source region gives a near source acceleration of at least 1.0 g. If the teleseismically estimated source depth of 51 km is assumed, the Acapulco accelerogram must be interpreted as composed of primarily body waves. This assumption yields a moment estimate of 3.3 ×1023 dyne-cm and a stress drop of 1.5 kbar. However, strong evidence indicates that the source depth is only about 1.0 km and that the record is composed mainly of high frequency (1.0 to 4.0 Hz) surface waves. The character of the record is that of a normally dispersed surface wave. The relatively simple form and high acceleration may be attributed to the high rigidity, crystalline rock types in the region. The three component record is fitted by summing the fundamental and first higher mode Rayleigh and Love waves using a model consisting of a single layer over a homogeneous half-space. The results are also checked using a direct wave-number integration program developed by Apsel and Luco. The moment estimate from the surface-wave synthetics is 2.0 ×1023 dyne-cm.

The effect of surficial sedimentary layers on continental surface waves

1958 ◽  
Vol 48 (4) ◽  
pp. 339-354 ◽  
Author(s):  
Jack Oliver ◽  
Maurice Ewing
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Frequency Component ◽  
The United States ◽  
High Frequency Component ◽  
Detailed Knowledge ◽  
Mode Propagation ◽  
Long Distance ◽  
Period Range ◽  
Short Period

Abstract Surface waves in the 1/2-second to 12-second period range, recorded at several stations in eastern North America from the eastern Tennessee shock of June 23, 1957, are the bases for several deductions concerning the effect of sedimentary layers on continental surface wave propagation. These are: (1) The velocities of surface waves of the fundamental Love and Rayleigh modes having periods less than about 10 seconds may be strongly affected by sedimentary layers of average thickness. The decrease in velocity accounts, at least in part, for the prolongation of surface-wave trains in this period range when sedimentary layers of appreciable thickness have been traversed. (2) Higher-mode propagation for both types of surface waves is a possible explanation for the velocities, frequencies, and amplitudes of the phase Sg at moderate epicentral distances, and of its long-distance counterpart the high-frequency component of Lg. The lower-frequency components of Lg have been explained previously by other aspects of normal-mode propagation in the crust. (3) Study of dispersion of short-period surface waves can result in fairly detailed knowledge of velocity-depth relation within the sedimentary column and may also reveal information on anisotropy. (4) The results of this study must bear heavily on studies of microseism propagation. As an example, the increase of microseismic activity along the entire east coast of the United States when a storm moves onto the continental shelf may be attributed to channeling of the waves in the deep sedimentary trough beneath the shelf.

Surface-wave magnitudes of Eurasian earthquakes and explosions

1975 ◽  
Vol 65 (3) ◽  
pp. 693-709 ◽  
Author(s):  
Otto W. Nuttli ◽  
So Gu Kim
Keyword(s):  
Surface Wave ◽  
Focal Mechanism ◽  
Rayleigh Waves ◽  
Body Wave ◽  
Focal Depth ◽  
Vertical Component ◽  
P Waves ◽  
Long Period ◽  
Short Period ◽  
Continental Interior

abstract Body-wave magnitudes, mb, and surface-wave magnitudes, MS, were determined for approximately 100 Eurasian events which occurred during the interval August through December 1971. Body-wave magnitudes were determined from 1-sec P waves recorded by WWSSN short-period, vertical-component seismographs at epicentral distances greater than 25°. Surface-wave magnitudes were determined from 20-sec Rayleigh waves recorded by long-period, vertical-component WWSSN and VLPE seismographs. The earthquakes had mb values ranging from 3.6 to 5.7. Of 96 presumed earthquakes studied, 6 lie in or near the explosion portion of an mb:MS plot. The explosion mb:MS curve was obtained from seven Eurasian events which had mb values ranging from 5.0 to 6.2 and MS values from 3.2 to 5.1. All six anomalous earthquakes were located in the interior of Asia, in Tibet, and in Szechwan and Sinkiang provinces of China. In general, oceanmargin earthquakes were found to have more earthquake-like mb:MS values than those occurring in the continental interior. Neither focal depth nor focal mechanism can explain the anomalous events.

Surface-wave constraints on the August 1, 1975, Oroville earthquake

1977 ◽  
Vol 67 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Robert S. Hart ◽  
Rhett Butler ◽  
Hiroo Kanamori
Keyword(s):  
Surface Wave ◽  
Rayleigh Waves ◽  
Body Wave ◽  
Source Parameters ◽  
The Body ◽  
Wave Radiation ◽  
Spectral Amplitude ◽  
Surface Wave Magnitude ◽  
Long Period ◽  
Short Period

abstract Observations of Love and Rayleigh waves on WWSSN and Canadian Network seismograms have been used to place constraints upon the source parameters of the August 1, 1975, Oroville earthquake. The 20-sec surface-wave magnitude is 5.6. The surface-wave radiation pattern is consistent with the fault geometry determined by the body-wave study of Langston and Butler (1976). The seismic moment of this event was determined to be 1.9 × 1025 dyne-cm by both time-domain and long-period (T ≥ 50 sec) spectral amplitude determinations. This moment value is significantly greater than that determined by short-period studies. This difference, together with the low seismic efficiency of this earthquake, indicates that the character of the source is intrinsically different at long periods from those aspects which dominate the shorter-period spectrum.

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