Source parameters from shallow events in the Rocky Mountain House earthquake swarm

1982 ◽  
Vol 19 (5) ◽  
pp. 907-918 ◽  
Author(s):  
C. J. Rebollar ◽  
E. R. Kanasewich ◽  
E. Nyland
Keyword(s):  
Source Parameters ◽  
Earthquake Swarm ◽  
Spectral Characteristics ◽  
High Stress ◽  
Rocky Mountain ◽  
P Wave ◽  
Digital Data ◽  
Integration Scheme ◽  
S Wave ◽  
Time Domains

We report here source parameters of the Rocky Mountain earthquake swarm derived from three-component digital data. During 6 days in October 1980, 21 events were recorded. Focal depths for these events are in the range of 1 ± 0.8 to 2 ± 2 km. Eleven events with local magnitudes from 2.1 to 2.8 yielded source parameters. Corner frequencies of the S-wave spectra were found in the range 6.2 ± 0.5 Hz, giving source dimensions of 160 ± 10 m. The corresponding P-wave corner frequencies are in the range 8.6 ± 3 Hz. The ratio of P to S corner frequencies varies from 0.9 to 2.1. There is a path effect between 13 and 16 Hz that could have affected these ratios. The average falloff over three components at high frequencies varies from −1.8 to −2.3. High stress drops, ranging from 47 to 263 bar (4.7–26.3 MPa), and apparent stresses, from 2.5 to 23 bar (0.25–2.3 MPa), were calculated. Five events have remarkably similar characteristics in the frequency and time domains. For these events the ratio of minimum strain energy W0, according to Kanamori, to the energy calculated using the integration scheme of Hanks and Thatcher was 3.7 ± 0.5. A theoretical value gives 3.1. The seismic efficiency ranges from 0.2 ± 0.04 to 0.17 ± 0.8. Large seismic moments for relatively small magnitudes were found. Some of these spectral characteristics are best explained as the result of displacement along a smooth fault.

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 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.

SEISMOLOGICAL AND ENGINEERING PARAMETERS OF 24 and 26 SEPTEMBER, 2019 MARMARA SEA EARTHQUAKES

2020 ◽  
Author(s):  
Eser Çakti ◽  
Fatma Sevil Malcioğlu ◽  
Hakan Süleyman
Keyword(s):  
Earthquake Engineering ◽  
Prediction Models ◽  
Source Parameters ◽  
Strong Motion ◽  
P Wave ◽  
Corner Frequency ◽  
Marmara Sea ◽  
S Wave ◽  
Data Set ◽  
The North

<p>On 24<sup>th</sup> and 26<sup>th</sup>  September 2019, two earthquakes of M<sub>w</sub>=4.5 and M<sub>w</sub>=5.6 respectively took place in the Marmara Sea. They were associated with the Central Marmara segment of the North Anatolian Fault Zone, which is pinpointed by several investigators as the most likely segment to rupture in the near future giving way to an earthquake larger than M7.0. Both events were felt widely in the region. The M<sub>w</sub>=5.6 event, in particular, led to a number of building damages in Istanbul, which were larger than expected in number and severity. There are several strong motion networks in operation in and around Istanbul. We have compiled a data set of recordings obtained at the stations of the Istanbul Earthquake Rapid Response and Early Warning operated by the Department of Earthquake Engineering of Bogazici University and of the National Strong Motion Network operated by AFAD. It consists of 148 three component recordings, in total.  444 records in the data set, after correction, were analyzed to estimate the source parameters of these events, such as corner frequency, source duration, radius and rupture area, average source dislocation and stress drop. Duration characteristics of two earthquakes were analyzed first by considering P-wave and S-wave onsets and then, focusing on S-wave and significant durations. PGAs, PGVs and SAs were calculated and compared with three commonly used ground motion prediction models (i.e  Boore et al., 2014; Akkar et al., 2014 and Kale et al., 2015). Finally frequency-dependent Q models were estimated using the data set and their validity was dicussed by comparing with previously developed models.</p>

scholarly journals Fault-zone waves observed at the southern Joshua Tree earthquake rupture zone

1994 ◽  
Vol 84 (3) ◽  
pp. 761-767
Author(s):  
S. E. Hough ◽  
Y. Ben-Zion ◽  
P. Leary
Keyword(s):  
Fault Zone ◽  
Wave Train ◽  
Spectral Characteristics ◽  
P Wave ◽  
S Wave ◽  
Low Velocity ◽  
Zone Structure ◽  
High Attenuation ◽  
Vertical Fault ◽  
Synthetic Waveform

Abstract Waveform and spectral characteristics of several aftershocks of the M 6.1 22 April 1992 Joshua Tree earthquake recorded at stations just north of the Indio Hills in the Coachella Valley can be interpreted in terms of waves propagating within narrow, low-velocity, high-attenuation, vertical zones. Evidence for our interpretation consists of: (1) emergent P arrivals prior to and opposite in polarity to the impulsive direct phase; these arrivals can be modeled as headwaves indicative of a transfault velocity contrast; (2) spectral peaks in the S wave train that can be interpreted as internally reflected, low-velocity fault-zone wave energy; and (3) spatial selectivity of event-station pairs at which these data are observed, suggesting a long, narrow geologic structure. The observed waveforms are modeled using the analytical solution of Ben-Zion and Aki (1990) for a plane-parallel layered fault-zone structure. Synthetic waveform fits to the observed data indicate the presence of NS-trending vertical fault-zone layers characterized by a thickness of 50 to 100 m, a velocity decrease of 10 to 15% relative to the surrounding rock, and a P-wave quality factor in the range 25 to 50.

Examining the processing differences between P and P-S waves in a Rocky Mountain Foothills model

2014 ◽  
Vol 54 (2) ◽  
pp. 504
Author(s):  
Sanjeev Rajput ◽  
Michael Ring
Keyword(s):  
Rocky Mountain ◽  
P Wave ◽  
S Wave ◽  
Converted Wave ◽  
Wave Source ◽  
Depth Migration ◽  
S Waves ◽  
Full Waveform ◽  
Fluid Saturation ◽  
Converted Waves

For the past two decades, most of the shear-wave (S-wave) or converted wave (P-S) acquisitions were performed with P-wave source by making the use of downgoing P-waves converting to upgoing S-waves at the mode conversion boundaries. The processing of converted waves requires studying asymmetric reflection at the conversion point, difference in geometries and conditions of source and receiver, and the partitioning of energy into orthogonally polarised components. Interpretation of P-S sections incorporates the identification of P-S waves, full waveform modeling, correlation with P-wave sections and depth migration. The main applications of P-S wave imaging are to obtain a measure of subsurface S-wave properties relating to rock type and fluid saturation (in addition to the P-wave values), imaging through gas clouds and shale diapers, and imaging interfaces with low P-wave contrast but significant S-wave changes. This study examines the major differences in processing of P and P-S wave surveys and the feasibility of identifying converted mode reflections by P-wave sources in anisotropic media. Two-dimensional synthetic seismograms for a realistic rocky mountain foothills model were studied. A Kirchhoff-based technique that includes anisotropic velocities is used for depth migration of converted waves. The results from depth imaging show that P-S section help in distinguishing amplitude associated with hydrocarbons from those caused by localised stratigraphic changes. In addition, the full waveform elastic modeling is useful in finding an appropriate balance between capturing high-quality P-wave data and P-S data challenges in a survey.

Joint hypocentral determination and the detection of low-velocity anomalies. An example from the Phlegraean Fields earthquakes

1990 ◽  
Vol 80 (1) ◽  
pp. 129-139 ◽  
Author(s):  
Jose Pujol ◽  
Richard Aster
Keyword(s):  
Earthquake Swarm ◽  
P Wave ◽  
S Wave ◽  
Time Data ◽  
Low Velocity ◽  
Data Set ◽  
Epicentral Area ◽  
Velocity Inversion ◽  
Phlegraean Fields ◽  
Velocity Anomalies

Abstract Arrival time data from the Phlegraean Fields (Italy) earthquake swarm recorded by the University of Wisconsin array in 1983 to 1984 were reanalyzed using a joint hypocentral determination (JHD) technique. The P- and S-wave station corrections computed as part of the JHD analysis show a circular pattern of central positive values surrounded by negative values whose magnitudes increase with distance from the center of the pattern. This center roughly coincides with the point of the maximum uplift (almost 2 m) associated with the swarm. Corrections range from −0.85 to 0.10 sec for P-wave arrivals and from −1.09 to 0.70 sec for S-wave arrivals. We interpret these patterns of corrections as caused by a localized low-velocity anomaly in the epicentral area, which agrees with the results of a previous 3-D velocity inversion of the same data set. The relocated (JHD) epicenters show less scatter than the epicenters obtained in the velocity inversion, and move more of the seismic activity to the vicinity of the only presently active fumarolic feature. The capability of the JHD technique to detect low-velocity anomalies and at the same time to give reliable locations, particularly epicenters, was verified using synthetic data generated for a 3-D velocity model roughly resembling the model obtained by velocity inversion.

Seismic impedance inversion and interpretation of a gas carbonate reservoir in the Alberta Foothills, western Canada

Geophysics ◽  
2003 ◽  
Vol 68 (5) ◽  
pp. 1460-1469 ◽  
Author(s):  
Gislain B. Madiba ◽  
George A. McMechan
Keyword(s):  
Rocky Mountain ◽  
Wave Impedance ◽  
Carbonate Reservoir ◽  
P Wave ◽  
Western Canada ◽  
S Wave ◽  
Data Set ◽  
Water Saturated ◽  
Gas Potential ◽  
Elastic Impedance

Acoustic and simultaneous elastic impedance inversions of a 2D land seismic data set are performed to characterize a carbonate reservoir of Mississippian age in the Turner Valley Formation, in the Rocky Mountain foothills of western Canada. The inversions produce P‐wave and S‐wave impedance sections (Ip and Is, respectively), from which Lamé parameter × density (λρ and μρ) sections are derived. The Ip data provide a separation between the clastics and carbonates. The μρ data provide an estimate of porosity distribution within the dolomitized limestone target. Deviations from baseline curves for water‐saturated carbonates, of λρ versus porosity, λ/μ versus porosity, and Is versus Ip, are interpreted as indicators of gas potential. These indicators all provide similar spatial patterns of areas of high gas potential and are consistent with the gas occurence observed in a well.

Source dynamics of two great earthquakes of the Indian subcontinent: The Bihar-Nepal earthquake of January 15, 1934 and the Quetta earthquake of May 30, 1935

1980 ◽  
Vol 70 (3) ◽  
pp. 757-773
Author(s):  
D. D. Singh ◽  
Harsh K. Gupta
Keyword(s):  
Main Shock ◽  
Indian Subcontinent ◽  
High Stress ◽  
P Wave ◽  
Wave Polarization ◽  
S Wave ◽  
Temporal And Spatial Variation ◽  
Regional Seismicity ◽  
Source Mechanisms ◽  
Temporal And Spatial

abstract Source mechanisms of two major destructive earthquakes which occurred at the Bihar-Nepal border and in the Quetta region on January 15, 1934 and May 30, 1935, respectively, are determined using the P-wave first motions, S-wave polarization angles, and surface-wave spectral data. The high stress drop and apparent stress associated with these events suggest that high tectonic stresses are prevailing in these regions. A major part of the stresses accumulated before the occurrence of the two earthquakes had been released through the main shock. An investigation of temporal and spatial variation of regional seismicity reveals possible existence of seismic gaps before the occurrence of these two major events.

Examining the processing differences between P and P-S waves in a Rocky Mountain Foothills model

2014 ◽  
Vol 54 (2) ◽  
pp. 536
Author(s):  
Sanjeev Rajput ◽  
Michael Ring
Keyword(s):  
Rocky Mountain ◽  
P Wave ◽  
S Wave ◽  
Converted Wave ◽  
Wave Source ◽  
Depth Migration ◽  
S Waves ◽  
Full Waveform ◽  
Fluid Saturation ◽  
Converted Waves

For the past two decades, most of the shear-wave (S-wave) or converted wave (P-S) acquisitions were performed with P-wave source by making the use of downgoing P-waves converting to upgoing S-waves at the mode conversion boundaries. The processing of converted waves requires studying asymmetric reflection at the conversion point, difference in geometries and conditions of source and receiver, and the partitioning of energy into orthogonally polarised components. Interpretation of P-S sections incorporates the identification of P-S waves, full waveform modeling, correlation with P-wave sections and depth migration. The main applications of P-S wave imaging are to obtain a measure of subsurface S-wave properties relating to rock type and fluid saturation (in addition to the P-wave values), imaging through gas clouds and shale diapers, and imaging interfaces with low P-wave contrast but significant S-wave changes. This study examines the major differences in processing of P and P-S wave surveys and the feasibility of identifying converted mode reflections by P-wave sources in anisotropic media. Two-dimensional synthetic seismograms for a realistic rocky mountain foothills model were studied. A Kirchhoff-based technique that includes anisotropic velocities is used for depth migration of converted waves. The results from depth imaging show that P-S section help in distinguishing amplitude associated with hydrocarbons from those caused by localised stratigraphic changes. In addition, the full waveform elastic modeling is useful in finding an appropriate balance between capturing high-quality P-wave data and P-S data challenges in a survey.

Nonlinear Multiple Earthquake Location and Velocity Estimation in the Canadian Rocky Mountain Trench

2020 ◽  
Vol 110 (6) ◽  
pp. 3103-3114
Author(s):  
Joshua Chris Shadday Purba ◽  
Jan Dettmer ◽  
Hersh Gilbert
Keyword(s):  
Prior Knowledge ◽  
Wave Velocity ◽  
Field Data ◽  
Velocity Ratio ◽  
Rocky Mountain ◽  
P Wave ◽  
Earthquake Location ◽  
S Wave ◽  
Data Noise ◽  
P Wave Velocity

ABSTRACT The calculation of earthquake hypocenters requires careful treatment, particularly when prior knowledge of the study area is limited. The prior knowledge, such as wave velocity and data noise, is often assumed to be known in earthquake location algorithms. Such assumptions can greatly simplify the inverse problem but are less general than nonlinear approaches. A nonlinear treatment is of particular importance when the uncertainty quantification of locations is of interest. We present a nonlinear multiple-earthquake location method that is applicable when little prior knowledge of the area exists. Efficient Markov chain Monte Carlo (MCMC) sampling is employed in conjunction with a hierarchical Bayesian model that treats earthquake hypocenter parameters, as well as P-wave velocity, ratio in P-/S-wave velocities, and P- and S-data noise standard deviations as unknown. Hypocenters for multiple earthquakes are located concurrently to provide sufficient constraints for the parameter’s P-wave velocity, ratio in P-/S-wave velocity, and P- and S-data noise standard deviations, which are shared among events. The algorithm is applied to simulated and field data. With field data, 47 event hypocenters are located in 1 yr of data from 10 sensors in the Canadian Rocky Mountain trench. To analyze the probabilistic solutions, we compare single-earthquake and multiple-earthquake locations for the 47 events and find that the multiple-earthquake location produces better-constrained solutions when compared with the single-event case. In particular, depth uncertainties are significantly reduced for the multiple-earthquake location. The algorithm is inexpensive, considering that it is based on an MCMC approach and highly objective, requiring little practitioner choice for tuning.

Sign in / Sign up

Export Citation Format

Share Document