Source characterization and fault plane determination for MbLg = 1.2 to 4.4 earthquakes in the Charlevoix Seismic Zone, Quebec, Canada

1995 ◽  
Vol 85 (6) ◽  
pp. 1604-1621 ◽  
Author(s):  
Yingping Li ◽  
Charles Doll ◽  
M. N. Toksöz
Keyword(s):  
Stress Drop ◽  
Dynamic Range ◽  
Fault Plane ◽  
Source Parameters ◽  
High Dynamic Range ◽  
Focal Mechanisms ◽  
P Wave ◽  
Seismic Zone ◽  
Source Characterization ◽  
Waveform Cross Correlation

Abstract Two earthquake doublets and two multiplets recorded by the Charlevoix Telemetered Network (CLTN) in the Charlevoix Seismic Zone (CSZ) of southern Quebec, Canada, have been analyzed using an empirical Green's function (EGF) method to derive the relative source time functions (RSTF's) of seven master events with MbLg = 1.2 to 4.4. We identified the doublets and multiplets using a waveform cross-correlation and relative event location technique to verify that each earthquake pair had similar focal mechanisms and hypocentral locations. Three-component S waveforms recorded by the high dynamic range (126 dB) instrumentation of the CLTN were used to extract the RSTF's. The RSTF's reveal that six of the seven events are simple with single-source pulses having durations of 0.05 to 0.2 sec. Another earthquake (920310-0545, M 3.3) appears to be a double event with two episodes of rupturing. Azimuthal variations of the RSTF pulse amplitudes and widths provide strong evidence for the rupture directivities of five of the earthquakes (M = 1.2 to 4.4). The azimuthal variations in the RSTF pulse amplitudes were used to estimate the rupture directions and rupture velocities. Lower-bound estimates of the rupture velocity range from 0.5 to 0.7 Vs. Estimates of the rupture direction were combined with P-wave focal mechanisms for the four largest events (M 3.3 to 4.4) to identify the fault plane for these earthquakes. Source parameters were measured for the RSTF's of the master events, including seismic moments of 3.5 × 1018 to 5.3 × 1021 dyne-cm, fault radii of 100 to 330 m, and static stress drops of 2 to 90 bars. The fault radii and stress-drop estimates for M > 3 events agree well with estimates obtained by other researchers for M ∼ 3 to 4.5 earthquakes in the CSZ. We also observed apparent scaling between the stress drop and the earthquake size, which has been reported in other studies of stress drop in northeastern North America.

Simultaneous inversion for Q and source parameters of microearthquakes accompanying hydraulic fracturing in granitic rock

1991 ◽  
Vol 81 (2) ◽  
pp. 553-575 ◽  
Author(s):  
Michael Fehler ◽  
W. Scott Phillips
Keyword(s):  
Hydraulic Fracturing ◽  
Stress Drop ◽  
Source Parameters ◽  
Low Frequency ◽  
Seismic Energy ◽  
P Wave ◽  
Corner Frequency ◽  
Spectral Amplitude ◽  
Seismic Zone ◽  
Stress Drops

Abstract An inversion that fits spectra of earthquake waveforms and gives robust estimates of corner frequency and low-frequency spectral amplitude has been used to determine source parameters of 223 microearthquakes induced by hydraulic fracturing in granodiorite. Assuming a ω−2 source model, the inversion fits the P-wave spectra of microearthquake waveforms to determine individual values of corner frequency and low-frequency spectral amplitude for each event and one average frequency-independent Q for all source-receiver paths. We also implemented a constraint that stress drops of all microearthquakes be similar but not equal and found that this constraint did not significantly degrade the quality of the fits to the spectra. The waveforms analyzed were recorded by a borehole seismometer. The P-wave Q was found to be 1070. For Q values as low as 600 and as high as 3000, the misfit between model and spectra increased by less than 5 per cent and the average corner frequency changed by less than 15 per cent from those obtained with a Q of 1070. Average stress drop was 3.7 bars. Seismic moments obtained from spectra ranged from 1013 to 1018 dyne-cm. The low stress drops are interpreted to result from underestimation of the actual stress drops because of a nonuniform distribution of stress drop and slip along the fault planes. Spatially varying stress drops and slips result from the strong rock heterogeneity due to the injection of fluid into the rock. Stress drops were found to be larger near the edges of the seismic zone, in regions that had not been seismically active during previous injections. The seismic moments determined from spectra were used to obtain a coda length-to-moment relation. Then, moments were estimated for 1149 events from measurements of coda lengths from events whose moments could not be measured from spectra because of saturation or a low signal-to-noise ratio. The constant of proportionality between cumulative number of events and seismic moment is higher than that found for tectonic regions. The slope is so high that the seismic energy release is dominated by the large number of small events. In the absence of information about the number of events smaller than we studied, we cannot estimate the total seismic energy released by the hydraulic injection.

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.

USGS Near‐Real‐Time Products—and Their Use—for the 2018 Anchorage Earthquake

2019 ◽  
Vol 91 (1) ◽  
pp. 94-113 ◽  
Author(s):  
Eric M. Thompson ◽  
Sara K. McBride ◽  
Gavin P. Hayes ◽  
Kate E. Allstadt ◽  
Lisa A. Wald ◽  
...  
Keyword(s):  
Media Coverage ◽  
Fault Plane ◽  
Source Parameters ◽  
Strong Motion ◽  
Source Characterization ◽  
Motion Data ◽  
Additional Information ◽  
Multiple Products ◽  
Earthquake Source Parameters ◽  
The Media

Abstract In the minutes to hours after a major earthquake, such as the recent 2018 Mw 7.1 Anchorage event, the U.S. Geological Survey (USGS) produces a suite of interconnected earthquake products that provides diverse information ranging from basic earthquake source parameters to loss estimates. The 2018 Anchorage earthquake is the first major domestic earthquake to occur since several new USGS products have been developed, thus providing an opportunity to discuss the newly expanded USGS earthquake product suite, its timeliness, performance, and reception. Overall, the products were relatively timely, accurate, well received, and widely used, including by the media, who used information and visualizations from many products to frame their early reporting. One downside of the codependence of multiple products is that reasonable updates to upstream products (e.g., magnitude and source characterization) can result in significant changes to downstream products; this was the case for the Anchorage earthquake. However, the coverage of strong‐motion stations and felt reports was so dense that the ShakeMap and downstream products were relatively insensitive to changes in magnitude or fault‐plane orientation once the ground‐motion data were available. Shaking and loss indicators initially fluctuated in the first hour or two after the earthquake, but they stabilized quickly. To understand how the products are being used and how effectively they are being communicated, we analyze the media coverage of USGS earthquake products. Most references to USGS products occurred within the first 48 hr after the event. The lack of coverage after 48 hr could indicate that longer‐term products addressing what actions the USGS is taking or what early reconnaissance has revealed might be useful for those people wanting additional information about the earthquake.

Inversion of regional surface-wave spectra for source parameters of aftershocks from the Loma Prieta earthquake

1991 ◽  
Vol 81 (5) ◽  
pp. 1726-1736
Author(s):  
Susan L. Beck ◽  
Howard J. Patton
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Focal Mechanism ◽  
Source Parameters ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
P Wave ◽  
Wave Spectra ◽  
Short Period ◽  
First Motion

Abstract Surface waves recorded at regional distances are used to study the source parameters for three of the larger aftershocks of the 18 October 1989, Loma Prieta, California, earthquake. The short-period P-wave first-motion focal mechanisms indicate a complex aftershock sequence with a wide variety of mechanisms. Many of these events are too small for teleseismic body-wave analysis; therefore, the regional surface-waves provide important long-period information on the source parameters. Intermediate-period Rayleigh- and Love-wave spectra are inverted for the seismic moment tensor elements at a fixed depth and repeated for different depths to find the source depth that gives the best fit to the observed spectra. For the aftershock on 19 October at 10:14:35 (md = 4.2), we find a strike-slip focal mechanism with right lateral motion on a NW-trending vertical fault consistent with the mapped trace of the local faults. For the aftershock on 18 October at 10:22:04 (md = 4.4), the surface waves indicate a pure reverse fault with the nodal planes striking WNW. For the aftershock on 19 October at 09:53:50 (md = 4.4), the surface waves indicate a strike-slip focal mechanism with a NW-trending vertical nodal plane consistent with the local strike of the San Andreas fault. Differences between the surface-wave focal mechanisms and the short-period P-wave first-motion mechanisms are observed for the aftershocks analyzed. This discrepancy may reflect the real variations due to differences in the band width of the two observations. However, the differences may also be due to (1) errors in the first-motion mechanism due to incorrect near-source velocity structure and (2) errors in the surface-wave mechanisms due to inadequate propagation path corrections.

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.

Spectral source parameters for weak local earthquakes in the Pannonian basin

2010 ◽  
Vol 2 (4) ◽  
Author(s):  
Bálint Süle
Keyword(s):  
Stress Drop ◽  
Seismic Moment ◽  
Pannonian Basin ◽  
Source Parameters ◽  
Active Regions ◽  
P Wave ◽  
Local Earthquakes ◽  
Scaling Relationship ◽  
Dynamic Source ◽  
Relationship Of

AbstractDynamic source parameters are estimated from P-wave displacement spectra for 18 local earthquakes (1.2 < ML < 3.7) that occurred in two seismically active regions of Hungary between 1995 and 2004. Although the geological setting of the two areas is quite different, their source parameters cannot be distinguished. The source dimensions range from 200 to 900 m, the seismic moment from 6.3x1011 to 3.48×1014 Nm, the stress drop from 0.13 to 6.86 bar, and the average displacement is less than 1 cm for all events. The scaling relationship between seismic moment and stress drop indicates a decrease in stress drop with decreasing seismic moment. A linear relationship of M w = 0.71 M L + 0.92 is obtained between local magnitude and moment magnitude.

An optimal strategy for searching the best fault-plane solution using wave-amplitude data

1977 ◽  
Vol 67 (5) ◽  
pp. 1355-1362
Author(s):  
Kailash Khattri
Keyword(s):  
Seismic Waves ◽  
Fault Plane ◽  
Source Parameters ◽  
P Wave ◽  
Spectral Amplitude ◽  
Fault Plane Solution ◽  
Amplitude Data ◽  
Earthquake Source Parameters ◽  
Plane Solution ◽  
Deep Focus

abstract This paper presents an optimum search procedure known as the Fibonacci Technique for abstracting the earthquake-source parameters from the amplitude data of seismic waves. The power of the method has been demonstrated by determining the fault-plane solution of a deep-focus earthquake using the P-wave spectral amplitude data.

scholarly journals Seismic Moment, Stress Drop, Strain Energy, Dislocation Radius, and Location of Seismic Acoustic Emissions Associated with a High Alpine Snowpack at Berthoud Pass, Colorado, U.S.A. (Abstract only)

1983 ◽  
Vol 4 ◽  
pp. 304-304
Author(s):  
Charles Cleland Rosé
Keyword(s):  
Stress Drop ◽  
Seismic Moment ◽  
Source Parameters ◽  
Acoustic Emissions ◽  
Body Waves ◽  
P Wave ◽  
Dissipated Energy ◽  
Fracture Area ◽  
Stress Drops ◽  
Predictive Indicator

The monitoring of the number of acoustic seismic impulses arising from snow instabilities is regarded as a relative indicator of an unstable snow slope but has not yielded a qualitative, predictive indicator. Until now, the source parameters (fracture area and length), seismic moment, energy released, stress drop, and location of acoustic seismic emissions arising from the snowpack have been neglected. A comprehension of these parameters leads to a better understanding of the event and may help in avalanche prediction.The location of a seismic event is derived from time differences between P-wave arrivals at four sensors located at the snow-ground interface. Three methods confirm the location of an acoustic seismic snow event to within 2 to 4 cm when the event is inside a seismic net.Spectral analyses of body waves from seismic snow events yield estimates of source parameters, stress drop and energy released. Equivalent dislocation surface radii range from 4.8 to 9.0 cm, which give stress drops of 0.20 to 0.29 bar, with a dissipated energy in the range of 0.0205 to 0.0632 J.Spectral analysis of the acoustic seismic snow event with application of dislocation theory provides several likely methods to predict avalanches of a climax type.

scholarly journals Seismic Moment, Stress Drop, Strain Energy, Dislocation Radius, and Location of Seismic Acoustic Emissions Associated with a High Alpine Snowpack at Berthoud Pass, Colorado, U.S.A. (Abstract only)

1983 ◽  
Vol 4 ◽  
pp. 304
Author(s):  
Charles Cleland Rosé
Keyword(s):  
Stress Drop ◽  
Seismic Moment ◽  
Source Parameters ◽  
Acoustic Emissions ◽  
Body Waves ◽  
P Wave ◽  
Dissipated Energy ◽  
Fracture Area ◽  
Stress Drops ◽  
Predictive Indicator

The monitoring of the number of acoustic seismic impulses arising from snow instabilities is regarded as a relative indicator of an unstable snow slope but has not yielded a qualitative, predictive indicator. Until now, the source parameters (fracture area and length), seismic moment, energy released, stress drop, and location of acoustic seismic emissions arising from the snowpack have been neglected. A comprehension of these parameters leads to a better understanding of the event and may help in avalanche prediction. The location of a seismic event is derived from time differences between P-wave arrivals at four sensors located at the snow-ground interface. Three methods confirm the location of an acoustic seismic snow event to within 2 to 4 cm when the event is inside a seismic net. Spectral analyses of body waves from seismic snow events yield estimates of source parameters, stress drop and energy released. Equivalent dislocation surface radii range from 4.8 to 9.0 cm, which give stress drops of 0.20 to 0.29 bar, with a dissipated energy in the range of 0.0205 to 0.0632 J. Spectral analysis of the acoustic seismic snow event with application of dislocation theory provides several likely methods to predict avalanches of a climax type.

Aftershocks of the 1952 Kern County, California, earthquake sequence

1999 ◽  
Vol 89 (4) ◽  
pp. 1094-1108 ◽  
Author(s):  
Douglas Dreger ◽  
Brian Savage
Keyword(s):  
Sierra Nevada ◽  
Dynamic Range ◽  
Moment Tensor ◽  
Source Parameters ◽  
High Dynamic Range ◽  
Earthquake Sequence ◽  
Seismic Moment Tensor ◽  
Kern County ◽  
Waveform Modeling ◽  
First Motion

Abstract We have studied the seismograms recorded at the historic Berkeley (BRK) and Pasadena (PAS) stations for 20 aftershocks of the 21 July 1952 Kern County earthquake sequence. These events, in the magnitude range of MW 4.5 to 5.6, are too small to be studied teleseismically, yet they are important for better understanding the tectonics of the southern Sierra Nevada and the Tehachapi Mountains. On-scale recordings of moderate-sized events from this important earthquake sequence were first scanned, digitized, and then subjected to waveform modeling using a seismic moment tensor inverse procedure. In particular, the long-period, three-component Galitzen instrument at BRK and the 6-sec Wood-Anderson at PAS provided very high quality seismograms that could be analyzed in this manner. These two sites have been continuously operated from 1887 and 1927, respectively, and both are current sites of state-of-the-art broadband, high dynamic range instrumentation. First-motion polarities reported by Bath and Richter (1958) were used as additional constraints in the estimation of source parameters. There is considerable variability in the three-component seismograms of the 1952 aftershocks, which in turn result in a diversity of focal mechanisms. The majority of the solutions are northwest-striking reverse mechanisms that likely occurred on various mapped thrust faults in the hanging block of the mainshock. There are several events with northeast-striking, left-lateral mechanisms that are consistent with the strike of the White Wolf fault, as well as several normal slip events. The results of this study indicate that there are a variety of active fault structures adjacent to the White Wolf, Garlock and San Andreas faults in this region.

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