Source parameters and scaling relationships of small earthquakes in the northeastern Caribbean

1981 ◽  
Vol 71 (4) ◽  
pp. 1173-1190
Author(s):  
Arthur Frankel
Keyword(s):  
Seismic Moment ◽  
Dynamic Stress ◽  
Source Parameters ◽  
Earthquake Swarm ◽  
Fold Increase ◽  
Virgin Islands ◽  
Scaling Relationships ◽  
Short Period ◽  
Relative Stress ◽  
Stress Drops

abstract The seismic moments and stress drops of 23 earthquakes (1.1 ≦ M ≦ 2.4) that occurred during an earthquake swarm in the Virgin Islands were determined from the analysis of their P waveforms. The data consist of digitally recorded seismograms collected by a short-period seismic network operating in the northeastern Caribbean. The events of the swarm are particularly useful for comparing the relative stress drops of small earthquakes, because their source to receiver paths and focal mechanisms are very similar. The static stress drops calculated for these earthquakes varied from about 0.2 to 2 bars. The data clearly illustrate that the static and dynamic stress drops of these earthquakes generally increased with the size (moment) of the events. The fault radii for these shocks increased with seismic moment, but only by a factor of 2 for a 100-fold increase in seismic moment. The velocity waveforms of the larger events were systematically more impulsive than those of the smaller earthquakes. These observations imply that, for this set of earthquakes, the final fault radius is a function of the stress drop that occurs during the rupture process.

Determination of source parameters of small earthquakes from P-wave rise time

1973 ◽  
Vol 63 (2) ◽  
pp. 599-614 ◽  
Author(s):  
M. E. O'Neill ◽  
J. H. Healy
Keyword(s):  
Rise Time ◽  
Source Parameters ◽  
P Wave ◽  
Simple Method ◽  
Zero Crossing ◽  
Basic Measurement ◽  
Earthquake Source Parameters ◽  
Short Period ◽  
Stress Drops

abstract A simple method of estimating source dimensions and stress drops of small earthquakes is presented. The basic measurement is the time from the first break to the first zero crossing on short-period seismograms. Graphs relating these measurements to rise time as a function of Q and instrument response permit an estimate of earthquake source parameters without the calculation of spectra. Tests on data from Rangely, Colorado, and Hollister, California, indicate that the method gives reasonable results.

Focal depths and source parameters of the Rocky Mountain House earthquake swarm from digital data at Edmonton

1984 ◽  
Vol 21 (10) ◽  
pp. 1105-1113 ◽  
Author(s):  
C. J. Rebollar ◽  
E. R. Kanasewich ◽  
E. Nyland
Keyword(s):  
Epicentral Distance ◽  
Source Parameters ◽  
Earthquake Swarm ◽  
Focal Depth ◽  
Rocky Mountain ◽  
Small Variation ◽  
B Value ◽  
Digital Data ◽  
The Difference ◽  
Stress Drops

Seismic records at Edmonton (EDM) and Suffield (SES) between January 1976 and February 1980 show 220 events with magnitudes less than 4 originating near Rocky Mountain House. Many of these events show well defined Sn, Sg, and Pg phases and a small variation in the difference of Sg − Sn and Sg − Pg. Analysis of the theoretical travel times using a structure determined for central Alberta yields an average focal depth of 20 ± 5 km and an average epicentral distance of 175 ± 5 km southwest of Edmonton for 40 of these events. Because Sn was not clear on the remainder, it was not possible to get focal depths for all the events.Seismic moments of 80 events with local magnitudes from 1.6 to 3.5 were found to be in the range of 6.6 ± 2 × 1018 to 7.9 ± 2 × 1020 dyn∙cm (6.6 ± 2 × 1013 to 7.9 ± 2 × 1015 N∙cm). A relationship between local magnitude and seismic moment was log (M0) = 1.3ML + 16.6. This is similar to that determined for California. Source radii, where they could be determined, were 500 ± 50 m and stress drops were 0.75 ± 0.75 bar (75 ± 75 kPa).The energy release of 263 events recorded at EDM from the Rocky Mountain House area was 5.6 × 1017 erg (5.6 × 1010 J). The b value for this earthquake swarm was 0.8, similar to that observed in other parts of western Canada.The depths of focus, the low stress drops, and the statistical similarity to other natural earthquake sequences suggest that at least part of the swarm is of a natural origin.

Source parameters of the Ensenada Bay earthquake swarm, Baja California, Mexico

1985 ◽  
Vol 22 (1) ◽  
pp. 126-132 ◽  
Author(s):  
Cecilio J. Rebollar
Keyword(s):  
Seismic Data ◽  
Strain Energy ◽  
High Strain ◽  
Source Parameters ◽  
Earthquake Swarm ◽  
Ground Displacement ◽  
Source Dimensions ◽  
Fault Type ◽  
Stress Drops ◽  
High Strain Energy

Seismic data collected from the Ensenada Bay earthquake swarm of late 1981 were used to calculate the spectra of ground displacement. Data from the stations of Ensenada (ENX) and Cerro Bola (CBX), at epicentral distances of 14 and 57 km, respectively, were used to evaluate source parameters. The focal depths determined for these events were less than 10 km. The focal mechanism was a strike-slip fault type, with the plane of motion striking N52°W, parallel to the Agua Blanca Fault. Seismic moments ranging from 3.44 × 1019 to 5.99 × 1020 dyn∙cm (3.44 × 1014 to 5.99 × 1015 N∙cm) were estimated for events with local magnitudes in the range 1.7–2.3. The source dimensions were found to be 186 ± 36 m and the stress drops between 3 and 66 bar (0.3 and 6.6 MPa), comparable to results obtained in previous studies of shallow events (depths <10 km). The Ensenada swarm could be attributed to a localized zone of high-strain energy at the intersection of two faults. Ratios of P to S corner frequencies were evident for only five events; they were 1.39 ± 0.38. Magnitude and seismic moment from other studies were compared with the Ensenada data in the range of magnitudes 0–3. All the data can be accommodated by log M0 = 1.5 ML + (16.9 ± 1.1). The Ensenada earthquake swarm and the Victoria earthquake swarm, which occurred in the Mexicali valley in 1978, have similar source radii and corner frequencies for the same range of seismic moments.

scholarly journals Northridge aftershocks, a source study with TERRAscope data

1997 ◽  
Vol 87 (4) ◽  
pp. 1024-1034 ◽  
Author(s):  
Xi J. Song ◽  
Donald V. Helmberger
Keyword(s):  
Wave Train ◽  
Depth Range ◽  
Long Period ◽  
Short Period ◽  
Relative Stress ◽  
Source Mechanisms ◽  
Extended Surface ◽  
San Fernando ◽  
Stress Drops ◽  
Selection Of

Abstract Broadband and long-period displacement waveforms from a selection of Northridge aftershocks recorded by the TERRAscope array are modeled to study source characteristics. Source mechanisms and moments are determined with long-period data using an algorithm developed by Zhao and Helmberger (1994). These results are compared with those by Hauksson et al. (1995) and Thio and Kanamori (1996). The width of the direct pulses at the nearest stations PAS and CALB are measured as indications of the source duration. Another measurement of the source-time functions of these earthquakes is obtained by comparing the short-period to long-period energy ratio in the data to that in the synthetics. These measurements are used to estimate the relative stress drop using a formula given by Cohn et al. (1982). The depth distribution of the relative stress drops indicates that the largest stress drops are in the depth range of 5 to 15 km for an aftershock population of 24 events. A correlation of extended surface wave train with source depth is demonstrated for paths crossing the San Fernando basin.

scholarly journals SOURCE PARAMETERS of STRONG EARTHQUAKES of the EARTH

2019 ◽  
pp. 292-298 ◽  
Author(s):  
L. Chepkunas ◽  
L. Malyanova
Keyword(s):  
Seismic Moment ◽  
Source Parameters ◽  
Dynamic Parameters ◽  
Strong Earthquakes ◽  
The Earth ◽  
The World ◽  
Stress Drops ◽  
Digital Equipment

For the 19 strongest earthquakes of Russia and the world the dynamic parameters: seismic moments, lengths of ruptures, stress drops, the values of motion in the source are brought. The spectra of Р-wave were calculated on records of IRIS-IDA digital equipment at stations Obninsk-OBN, Talay-TLY, Kislovodsk-KIV in the range of epitsentralny distances of =25–82°. On the basis of the values of seismic moment Мo received on digital records at stations Obninsk-OBN, Talay-TLY, Kislovodsk-KIV, the momentny magnitude Mw (Kana-mori) are presented.

scholarly journals Fast and Robust Earthquake Source Spectra and Moment Magnitudes from Envelope Inversion

2021 ◽  
Author(s):  
Tom Eulenfeld ◽  
Torsten Dahm ◽  
Sebastian Heimann ◽  
Ulrich Wegler
Keyword(s):  
Source Parameters ◽  
Earthquake Swarm ◽  
Earthquake Source ◽  
Body Waves ◽  
Corner Frequency ◽  
Data Set ◽  
Displacement Spectra ◽  
Short Period ◽  
Source Spectra ◽  
Good Agreement

ABSTRACT With the present study, we introduce a fast and robust method to calculate the source displacement spectra of small earthquakes on a local to regional scale. The work is based on the publicly available Qopen method of full envelope inversion, which is further tuned for the given purpose. Important source parameters—seismic moment, moment magnitude, corner frequency, and high-frequency fall off—are determined from the source spectra by fitting a simple earthquake source model. The method is demonstrated by means of a data set comprising the 2018 West Bohemia earthquake swarm. We report moment magnitudes, corner frequencies, and centroid moment tensors inverted from short-period body waves with the Grond package for all earthquakes with a local magnitude larger than 1.8. Moment magnitudes calculated by envelope inversion show a very good agreement to moment magnitudes resulting from the probabilisitc moment tensor inversion. Furthermore, source displacement spectra from envelope inversion show a good agreement with spectra obtained by multiple taper analysis of the direct onsets of body waves but are not affected by the large scatter of the second. The seismic moments obtained with the envelope inversion scale with corner frequencies according to M0∝fc−4.7. Earthquakes of the present data set result in a smaller stress drop for smaller magnitudes. Self-similarity of earthquake rupture is not observed. In addition, we report frequency-dependent site amplification at the used stations.

Scaling relations between seismic moment and rupture area of earthquakes in stable continental regions

2021 ◽  
pp. 875529302098802
Author(s):  
Paul Somerville
Keyword(s):  
Seismic Moment ◽  
Source Parameters ◽  
Scaling Relations ◽  
Scale Invariant ◽  
Intraplate Earthquakes ◽  
Rupture Area ◽  
Earthquake Source Parameters ◽  
Stable Continental Regions ◽  
Self Similar ◽  
Stress Drops

This article describes the development of scaling relations between seismic moment and rupture area of earthquakes in stable continental regions (SCRs). The article reviews the relations developed by Somerville and compares them with relations developed by other investigators. It also compares the scaling relations of SCR earthquakes with those in tectonically active continental regions (TCRs). Three different methods of estimating rupture area, based on aftershocks, slip models, and duration methods were used by Somerville to analyze the relation between seismic moment and rupture area, using earthquake source parameters compiled from published literature. For each category of data, the relations obtained were not significantly different from those obtained by constraining them to be self-similar (scale-invariant), so self-similar relations were adopted. The stress drops corresponding to these scaling relations range from 51 to 86 bars, with an average of 65 bars. This value is comparable with the value of 58 bars obtained by Leonard, and it is recommended that the Leonard scaling relations for SCR earthquakes be used for the NGA East Project. To a first approximation, the results of Somerville and those of Somerville et al. indicate that the rupture areas of SCR earthquakes are about half those of TCR earthquakes, and their stress drops are about 2.8 times higher. Allmann and Shearer find less of a difference, presumably because their intraplate category includes some earthquakes that we would assign to TCR instead of SCR. Their study indicates that the rupture areas of intraplate earthquakes are about two-thirds those of TCR earthquakes, and their stress drops are about 2 times higher.

High stress drops of short-period subevents from the 1968 Tokachi-Oki earthquake as observed on strong-motion records

1984 ◽  
Vol 74 (5) ◽  
pp. 1529-1544
Author(s):  
Jim Mori ◽  
Kunihiko Shimazaki
Keyword(s):  
Source Parameters ◽  
High Stress ◽  
Strong Motion ◽  
P Waves ◽  
Strong Motion Records ◽  
Source Dimensions ◽  
Short Period ◽  
High Dynamic ◽  
Stress Drops ◽  
Very High

Abstract Strong-motion records of the 1968 Tokachi-Oki earthquake were examined, and two very high stress drop subevents were identified. The first subevent had been previously located by Nagamune (1969), and the second subevent was located in this study using P waves recorded on short-period WWSSN records. Estimates of source parameters revealed small source dimensions (&lt;1 per cent of the aftershock area) and very high dynamic and static stress drops in the kilobar range for both of the subevents. It is suggested that these subevents are important in driving the main rupture of this earthquake. The two subevents also produced the dominant accelerations on the strong-motion records, and it is shown that high-peak accelerations (150 to 200 cm/sec2) were recorded even at relatively large distances (100 to 200 km).

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.

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