scholarly journals The source mechanism of the August 7, 1966 El Golfo earthquake

1978 ◽  
Vol 68 (5) ◽  
pp. 1281-1292
Author(s):  
John E. Ebel ◽  
L. J. Burdick ◽  
Gordon S. Stewart
Keyword(s):  
Surface Wave ◽  
Stress Drop ◽  
Gulf Of California ◽  
Body Wave ◽  
Source Parameters ◽  
High Stress ◽  
Plate Boundary ◽  
The Body ◽  
Body Waves ◽  
Wave Radiation

abstract The El Golfo earthquake of August 7, 1966 (mb = 6.3, MS = 6.3) occurred near the mouth of the Colorado River at the northern end of the Gulf of California. Synthetic seismograms for this event were computed for both the body waves and the surface waves to determine the source parameters of the earthquake. The body-wave model indicated the source was a right lateral, strike-slip source with a depth of 10 km and a far-field time function 4 sec in duration. The body-wave moment was computed to be 5.0 × 1025 dyne-cm. The surface-wave radiation pattern was found to be consistent with that of the body waves with a surface-wave moment of 6.5 × 1025 dyne-cm. The agreement of the two different moments indicates that the earthquake had a simple source about 4 sec long. A comparison of this earthquake source with the Borrego Mountain and Truckee events demonstrates that all three of these earthquakes behaved as high stress-drop events. El Golfo was shown to be different from the low stress-drop, plate-boundary events which were located on the Gibbs fracture zone in 1967 and 1974.

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.

Source mechanism and surface-wave attenuation studies for Tibet earthquake of July 14, 1973

1979 ◽  
Vol 69 (3) ◽  
pp. 737-750
Author(s):  
D. D. Singh ◽  
Harsh K. Gupta
Keyword(s):  
Surface Wave ◽  
Stress Drop ◽  
Wave Attenuation ◽  
Source Parameters ◽  
High Stress ◽  
The Body ◽  
P Wave ◽  
Slip Angle ◽  
Apparent Stress ◽  
Crust And Upper Mantle

abstract Focal mechanism for Tibet earthquake of July 14, 1973 (M = 6.9, mb = 6.0) has been determined using the P-wave first motions, S-wave polarization angles, and surface-wave spectral data. A normal faulting is obtained with a plane having strike N3°W, dip 51°W, and slip angle 81°. The source parameters have been estimated for this event using the body- and surface-wave spectra. The seismic moment, fault length, apparent stress, stress drop, seismic energy release, average dislocation, and fault area are estimated to be 2.96 × 1026 dyne-cm, 27.4 km, 14 bars, 51 bars, 1.4 × 1022 ergs, 157 cm, and 628 km2, respectively. The high stress drop and apparent stress associated with this earthquake indicate that the high stresses are prevailing in this region. The specific quality factor Q is found to vary from 21 to 1162 and 22 to 1110 for Rayleigh and Love waves, respectively. These wide ranges of variation in the attenuation data may be due to the presence of heterogeneity in the crust and upper mantle.

Focal mechanism and source depth of earthquakes from body- and surface-wave data

1971 ◽  
Vol 61 (5) ◽  
pp. 1369-1379 ◽  
Author(s):  
Nezihi Canitez ◽  
M. Nafi Toksöz
Keyword(s):  
Surface Wave ◽  
Body Wave ◽  
Source Parameters ◽  
Focal Depth ◽  
Spectral Ratio ◽  
The Body ◽  
Spectral Ratios ◽  
Motion Data ◽  
Wave Data ◽  
Surface Wave Data

abstract The determination of focal depth and other source parameters by the use of first-motion data and surface-wave spectra is investigated. It is shown that the spectral ratio of Love to Rayleigh waves (L/R) is sensitive to all source parameters. The azimuthal variation of the L/R spectral ratios can be used to check the fault-plane solution as well as for focal depth determinations. Medium response, attenuation, and source finiteness seriously affect the absolute spectra and introduce uncertainty into the focal depth determinations. These effects are nearly canceled out when L/R amplitude ratios are used. Thus, the preferred procedure for source mechanism studies of shallow earthquakes is to use jointly the body-wave data, absolute spectra of surface waves, and the Love/Rayleigh spectral ratios. With this procedure, focal depths can be determined to an accuracy of a few kilometers.

scholarly journals Inversion of the body waves from the Borrego Mountain earthquake to the source mechanism

1976 ◽  
Vol 66 (5) ◽  
pp. 1485-1499 ◽  
Author(s):  
L. J. Burdick ◽  
George R. Mellman
Keyword(s):  
Body Wave ◽  
High Stress ◽  
Time Function ◽  
The Body ◽  
Body Waves ◽  
Polarization Angle ◽  
Long Period ◽  
Amplitude Data ◽  
Short Period ◽  
Wide Range

abstract The generalized linear inverse technique has been adapted to the problem of determining an earthquake source model from body-wave data. The technique has been successfully applied to the Borrego Mountain earthquake of April 9, 1968. Synthetic seismograms computed from the resulting model match in close detail the first 25 sec of long-period seismograms from a wide range of azimuths. The main shock source-time function has been determined by a new simultaneous short period-long period deconvolution technique as well as by the inversion technique. The duration and shape of this time function indicate that most of the body-wave energy was radiated from a surface with effective radius of only 8 km. This is much smaller than the total surface rupture length or the length of the aftershock zone. Along with the moment determination of Mo = 11.2 ×1025 dyne-cm, this radius implies a high stress drop of about 96 bars. Evidence in the amplitude data indicates that the polarization angle of shear waves is very sensitive to lateral structure.

scholarly journals Teleseismic analysis of the 1980 Mammoth Lakes earthquake sequence

1982 ◽  
Vol 72 (4) ◽  
pp. 1093-1109
Author(s):  
Jeffrey W. Given ◽  
Terry C. Wallace ◽  
Hiroo Kanamori
Keyword(s):  
Surface Wave ◽  
Sierra Nevada ◽  
Body Wave ◽  
The Body ◽  
Body Waves ◽  
Earthquake Sequence ◽  
Local Data ◽  
Fault Plane Solutions ◽  
Principal Axes ◽  
Mammoth Lakes

abstract The source mechanisms of the three largest events of the 1980 Mammoth Lakes earthquake sequence have been determined using surface waves recorded on the global digital seismograph network and the long-period body waves recorded on the WWSSN network. Although the fault-plane solutions from local data (Cramer and Toppozada, 1980; Ryall and Ryall, 1981) suggest nearly pure left-lateral strike-slip on north-south planes, the teleseismic waveforms require a mechanism with oblique slip. The first event (25 May 1980, 16h 33m 44s) has a mechanism with a strike of N12°E, dip of 50°E, and a rake of −35°. The second event (27 May 19h 44m 51s) has a mechanism with a strike of N15°E, dip of 50°, and a slip of −11°. The third event (27 May, 14h 50m 57s) has a mechanism with a strike of N22°E, dip of 50°, and a rake of −28°. The first event is the largest and has a moment of 2.9 × 1025 dyne-cm. The second and third events have moments of 1.3 and 1.1 × 1025 dyne-cm, respectively. The body- and surface-wave moments for the first and third events agree closely while for the second event the body-wave moment (approximately 0.6 × 1025 dyne-cm) is almost a factor of 3 smaller than the surface-wave moment. The principal axes of extension of all three events is in the approximate direction of N65°E which agrees with the structural trends apparent along the eastern front of the Sierra Nevada.

A Discussion on the measurement and interpretation of changes of strain in the Earth - Derivation of rupture area and stress-drop from body wave displacement spectra and the relative material strength in deep seismic zones

1973 ◽  
Vol 274 (1239) ◽  
pp. 361-368
Keyword(s):  
Stress Drop ◽  
Body Wave ◽  
Source Parameters ◽  
Source Area ◽  
Great Depth ◽  
Body Waves ◽  
Material Strength ◽  
Seismic Zone ◽  
Rupture Area ◽  
The Moment

The seismic moment and source area of an earthquake can be determined by fitting theoretical displacement amplitude spectra to observed ones. From these basic parameters the dislocation at the source and the stress-drop can be estimated. This method was tested in the case of four earthquakes for which the source parameters were known from observed surface ruptures. The uncertainty in the moment and area determinations was found to be approximately a factor of 2; for the displacement and stress-drop it was approximately a factor of 3 and 5 respectively. The application of spectral analysis of body waves to earthquakes in the deep seismic zone of Tonga-Kermadec indicate that stress-drop as well as apparent stress increase with depth and decrease again at great depth. This observation is interpreted as reflecting increasing material strength in the deep seismic zone near 450 km, with a reduction of strength at still greater depths. It is proposed that the temperature distribution in the downgoing slab of lithosphere causes this pattern.

scholarly journals Seismic Characterization of the Nevada National Security Site Using Joint Body Wave, Surface Wave, and Gravity Inversion

2019 ◽  
Vol 110 (1) ◽  
pp. 110-126
Author(s):  
Leiph Preston ◽  
Christian Poppeliers ◽  
David J. Schodt
Keyword(s):  
Surface Wave ◽  
National Security ◽  
Surface Waves ◽  
Body Wave ◽  
Wave Dispersion ◽  
The Body ◽  
Body Waves ◽  
Gravity Inversion ◽  
Surface Wave Dispersion ◽  
Near Surface

ABSTRACT As a part of the series of Source Physics Experiments (SPE) conducted on the Nevada National Security Site in southern Nevada, we have developed a local-to-regional scale seismic velocity model of the site and surrounding area. Accurate earth models are critical for modeling sources like the SPE to investigate the role of earth structure on the propagation and scattering of seismic waves. We combine seismic body waves, surface waves, and gravity data in a joint inversion procedure to solve for the optimal 3D seismic compressional and shear-wave velocity structures and earthquake locations subject to model smoothness constraints. Earthquakes, which are relocated as part of the inversion, provide P- and S-body-wave absolute and differential travel times. Active source experiments in the region augment this dataset with P-body-wave absolute times and surface-wave dispersion data. Dense ground-based gravity observations and surface-wave dispersion derived from ambient noise in the region fill in many areas where body-wave data are sparse. In general, the top 1–2 km of the surface is relatively poorly sampled by the body waves alone. However, the addition of gravity and surface waves to the body-wave dataset greatly enhances structural resolvability in the near surface. We discuss the methodology we developed for simultaneous inversion of these disparate data types and briefly describe results of the inversion in the context of previous work in the region.

Tectonic stress and the source mechanism of the Imperial Valley, California, earthquake of 1940

1972 ◽  
Vol 62 (5) ◽  
pp. 1283-1302 ◽  
Author(s):  
M. D. Trifunac
Keyword(s):  
Stress Drop ◽  
Body Wave ◽  
Strong Motion ◽  
Tectonic Stress ◽  
The Body ◽  
Body Waves ◽  
Imperial Valley ◽  
Multiple Sequence ◽  
Field Notes ◽  
Instrumental Records

Abstract The Imperial Valley earthquake was a multiple sequence (Trifunac and Brune, 1970) with at least four events occurring during the main energy release. These four events, recorded on the strong-motion seismograph in El Centro, located about 10 km NW from the instrumentally determined epicenter, and nine aftershocks recorded in the next 5 min are re-examined in this paper to test an approximate source theory (Brune, 1970). This theory predicts the shape of the body-wave spectra in terms of the seismic moment and stress drop. By fitting theoretical spectra to the spectra calculated from the strong-motion accelerogram, moment and stress drop can be estimated for each of the multiple events. Inasmuch as the average displacements at the fault and the source dimensions can be derived from the known moment and stress drop, the pattern of average displacements along the fault was computed from the instrumental records. A test of the theory, then, consists of comparing the fault displacements derived from seismograms with the fault displacements observed at the surface (Buwalda, unpublished field notes). For the Imperial Valley earthquake, agreement between these two independent methods of measurement is good, suggesting that the above theory is an adequate first approximation for the spectra of body waves. The stress drop variations along the fault, inferred also from the above theory, indicate two areas of major stress concentration located near the northwestern and southeastern ends of the dislocation. The stress drops for various events varied from about ten to several hundred bars.

Bias in surface-wave magnitude Ms due to inadequate distance corrections

1998 ◽  
Vol 88 (1) ◽  
pp. 43-61
Author(s):  
Mehdi Rezapour ◽  
Robert G. Pearce
Keyword(s):  
Surface Wave ◽  
Wave Amplitude ◽  
Body Wave ◽  
The Body ◽  
Body Waves ◽  
P Wave ◽  
Systematic Bias ◽  
Surface Wave Magnitude ◽  
Distance Curve ◽  
Distance Correction

Abstract We investigate bias in surface-wave magnitude using the complete ISC and NEIC datasets from 1978 to 1993. We conclude that although there are some small differences between the ISC and NEIC magnitudes, there is no major difference between these agencies for this presentation of the global dataset. The frequency-distance plot for reported surface-wave amplitude observations exhibits detailed structure of the body-wave amplitude-distance curve at all distances; the influence of the surface-wave amplitude decay with distance is much less apparent. This censoring via the body waves represents a large deficit in the number of potentially usable surface-wave amplitude observations, particularly in the P-wave shadow zone between Δ = 100° and 120°. We have obtained two new modified Ms formulas based upon analysis of all ISC data between 1978 and 1993. In the first, the conventional logarithmic dependence of the distance correction is retained, and we obtain M s e = log ( A / T ) max + 1.155 log ( Δ ) + 4.269 . In the second, we make allowance for the theoretically known contribution of dispersion and geometrical spreading, to obtain M s t = log ( A / T ) max + 1 3 log ( Δ ) + 1 2 log ( sin Δ ) + 0.0046 Δ + 5.370. Comparison of these formulas with other work confirms the inadequacy of the distance-dependence term in the Gutenberg and Prague formulas, and we show that our first formula, as well as that of Herak and Herak, gives less bias at all epicentral distances to within the scatter of the observed dataset. Our second formula provides an improved overall distance correction, especially beyond Δ = 145°. We show evidence that Airy-phase distance decay predominates at shorter distances (Δ≦30°), but for greater distances, we are unable to resolve whether this or non-Airy-phase decay predominates. Assuming 20-sec surface waves with U = 3.6 km/sec, we obtain a globally averaged apparent Q−1 of 0.00192 ± 0.00026 (Q ≈ 500). We argue that our second formula not only improves the distance correction for surface-wave magnitudes but also promotes the analysis of unexplained amplitude anomalies by formally allowing for those contributions that are theoretically predictable. We conclude that there remains systematic bias in station magnitudes and that this includes the effects of source depth, different path contributions, and differences in seismometer response. For intermediate magnitudes, Mts shows less scatter against log M0 than does Ms calculated using the Prague formula.

scholarly journals Imaging the subsurface using induced seismicity and ambient noise: 3-D tomographic Monte Carlo joint inversion of earthquake body wave traveltimes and surface wave dispersion

2020 ◽  
Vol 222 (3) ◽  
pp. 1639-1655
Author(s):  
Xin Zhang ◽  
Corinna Roy ◽  
Andrew Curtis ◽  
Andy Nowacki ◽  
Brian Baptie
Keyword(s):  
Surface Wave ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Joint Inversion ◽  
Body Wave ◽  
Source Parameters ◽  
Wave Dispersion ◽  
Inversion Method ◽  
Surface Wave Dispersion ◽  
Wave Data

SUMMARY Seismic body wave traveltime tomography and surface wave dispersion tomography have been used widely to characterize earthquakes and to study the subsurface structure of the Earth. Since these types of problem are often significantly non-linear and have non-unique solutions, Markov chain Monte Carlo methods have been used to find probabilistic solutions. Body and surface wave data are usually inverted separately to produce independent velocity models. However, body wave tomography is generally sensitive to structure around the subvolume in which earthquakes occur and produces limited resolution in the shallower Earth, whereas surface wave tomography is often sensitive to shallower structure. To better estimate subsurface properties, we therefore jointly invert for the seismic velocity structure and earthquake locations using body and surface wave data simultaneously. We apply the new joint inversion method to a mining site in the United Kingdom at which induced seismicity occurred and was recorded on a small local network of stations, and where ambient noise recordings are available from the same stations. The ambient noise is processed to obtain inter-receiver surface wave dispersion measurements which are inverted jointly with body wave arrival times from local earthquakes. The results show that by using both types of data, the earthquake source parameters and the velocity structure can be better constrained than in independent inversions. To further understand and interpret the results, we conduct synthetic tests to compare the results from body wave inversion and joint inversion. The results show that trade-offs between source parameters and velocities appear to bias results if only body wave data are used, but this issue is largely resolved by using the joint inversion method. Thus the use of ambient seismic noise and our fully non-linear inversion provides a valuable, improved method to image the subsurface velocity and seismicity.

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