A theoretical study of the radiation from small strikeslip earthquakes at close distances

1983 ◽  
Vol 73 (1) ◽  
pp. 83-96 ◽  
Author(s):  
Michel Campillo ◽  
Michel Bouchon
Keyword(s):  
Ground Motion ◽  
Epicentral Distance ◽  
Homogeneous Medium ◽  
Source Model ◽  
Strike Slip ◽  
Peak Ground Velocity ◽  
Corner Frequency ◽  
Crack Model ◽  
Sharp Change ◽  
S Wave

abstract We present a study of the seismic radiation of a physically realistic source model—the circular crack model of Madariaga—at close distance range and for vertically heterogeneous crustal structures. We use this model to represent the source of small strike-slip earthquakes. We show that the characteristics of the radiated seismic spectra, like the corner frequency, are strongly affected by the presence of the free surface and by crustal layering, and that they can be considerably different from the ones of the homogeneous-medium far-field solution. The vertical and radial displacement spectra are the most strongly affected. We use this source model to calculate the decay of peak ground velocity with epicentral distance and source depth for small strike-slip earthquakes in California. For distances between 10 and 80 km, the peak horizontal velocity decay is of the form r−1.25 for a 4-km hypocentral depth and r−1.65 for deeper sources. The predominance of supercritically reflected arrivals beyond epicentral distances of 70 to 80 km produces a sharp change in the rate of decay of the ground motion. For most of the cases considered, the peak ground velocity increases between 80 and 100 km. We also show that the S-wave velocity in the source layer is the lower limit of phase velocities associated with significant ground motion.

Source parameter analysis from strong motion records of the Friuli, Italy, earthquake sequence (1976-1977)

1987 ◽  
Vol 77 (4) ◽  
pp. 1127-1146
Author(s):  
Giuseppe De Natale ◽  
Raul Madariaga ◽  
Roberto Scarpa ◽  
Aldo Zollo
Keyword(s):  
Frequency Domain ◽  
Stress Drop ◽  
High Frequency ◽  
Epicentral Distance ◽  
Strong Motion ◽  
Source Model ◽  
Parameter Analysis ◽  
Corner Frequency ◽  
Spectral Parameters ◽  
Single Station

Abstract Time and frequency domain analyses are applied to strong motion data recorded in Friuli, Italy, during 1976 to 1977. An inversion procedure to estimate spectral parameters (low frequency level, corner frequency, and high frequency decay) has been applied to displacement spectra using a simple earthquake source model with a single corner frequency. The data were digitized accelerograms from ENEA-ENEL portable and permanent networks. Instrument-corrected SH waves were selected from a set of 138 three-component, hand-digitized records and 28 automatically digitized records. Thirty-eight events with stations having 8 to 32 km epicentral distance were studied. Different stress drop estimates were performed showing high values (200 to 300 bars, on the average) with seismic moments ranging from 2.8 × 1022 to 8.0 × 1024 dyne-cm. The observation of systematic higher values of Brune stress drop (obtained from corner frequencies) with respect to other time and frequency domain estimates of stress release, and the evidence on time series of multiple rupture episodes suggest that the observed corner frequencies are most probably related to subevent ruptures rather than the overall fault size. Seven events recorded at more than one station show a good correlation between rms, Brune, and dynamic stress drops, and a constant scaling of this parameter as a function of the seismic moment. When single station events are also considered, a slight moment dependence of these three stress drop estimates is observed differently. This may be explained by an inadequacy of the ω−2 high-frequency decay of the source model or by high-frequency attenuation due to propagation effects. The high-frequency cutoff of acceleration spectra indicates the presence of an Fmax in the range of 5 to 14 Hz, except for the stations where local site effects produce spectral peaks.

Ground Motion From A Magnitude 3.5 Earthquake Near Massena, New York: Evidence For Poor Resolution of Corner Frequency For Small Events

1989 ◽  
Vol 60 (3) ◽  
pp. 95-100 ◽  
Author(s):  
S.E. Hough ◽  
K. Jacob ◽  
R. Busby ◽  
P.A. Friberg
Keyword(s):  
Earthquake Engineering ◽  
Epicentral Distance ◽  
Wave Spectrum ◽  
P Wave ◽  
Corner Frequency ◽  
Source Spectrum ◽  
Wave Spectra ◽  
S Wave ◽  
High Quality ◽  
Wide Range

Abstract We present analysis of a magnitude 3.5 event which occurred at 9 km epicentral distance from a digital strong motion instrument operated by the National Center for Earthquake Engineering Research. Although the size of this isolated event is such that it can scarcely be considered to be a significant earthquake, a careful analysis of this high quality recording does yield several interesting results: 1) the S-wave spectra can be interpreted in terms of a simple omega-squared source spectrum and frequency-independent attenuation, 2) there is the suggestion of a poorly-resolved resonance in the P-wave spectrum, and perhaps most importantly, 3) the apparently simple S-wave spectra can be fit almost equally well with a surprisingly wide range of seismic corner frequencies, from roughly 5 to 25 Hz. This uncertainty in corner frequency translates into uncertainties in inferred Q values of almost an order of magnitude, and into uncertainties in stress drop of two orders of magnitude. Given the high quality of the data and the short epicentral distance to the station, we consider it likely that resolution of spectral decay and corner frequency will be at least as poor for any other recording of earthquakes with comparable or smaller magnitudes.

scholarly journals Seismological and Engineering Characteristics of Strong Motion Data from 24 and 26 September 2019 Marmara Sea Earthquakes

2021 ◽  
Author(s):  
Fatma Sevil Malcıoğlu ◽  
Hakan Süleyman ◽  
Eser Çaktı
Keyword(s):  
Ground Motion ◽  
Prediction Models ◽  
Strong Motion ◽  
P Wave ◽  
Corner Frequency ◽  
Marmara Region ◽  
Marmara Sea ◽  
S Wave ◽  
Data Set ◽  
Motion Data

Abstract An MW 4.5 earthquake took place on September 24, 2019 in the Marmara Sea. Two days after, on September 26, 2019, Marmara region was rattled by an MW5.7 earthquake. With the intention of compiling an ample strong ground motion data set of recordings, we have utilized the stations of Istanbul Earthquake Rapid Response and Early Warning System operated by the Department of Earthquake Engineering of Boğaziçi University and of the National Strong Motion Network operated by AFAD. All together 438 individual records are used to calculate the source parameters of events; namely, corner frequency, radius, rupture area, average source dislocation, source duration and stress drop. Some of these parameters are compared with empirical relationships and discussed extensively. Duration characteristics are analyzed in two steps; first, by making use of the time difference between P-wave and S-wave onsets and then, by considering S-wave durations and significant durations. It is observed that they yield similar trends with global models. PGA, PGV and SA values are compared with three commonly used ground motion prediction models. At distances closer than about 60 km observed intensity measures mostly conform with the GMPE predictions. Beyond 60 km their attenuation is clearly faster than those of GMPEs. Frequency-dependent Q models are developed for both events. Their consistency with existing regional models are confirmed.

Source parameters and scaling laws of the 1978 Swabian Jura (southwest Germany) aftershocks

1983 ◽  
Vol 73 (5) ◽  
pp. 1321-1343
Author(s):  
Frank Scherbaum ◽  
Dieter Stoll
Keyword(s):  
Scaling Laws ◽  
Source Parameters ◽  
Source Model ◽  
Local Network ◽  
Corner Frequency ◽  
Strong Increase ◽  
Crack Model ◽  
Data Set ◽  
Stress Drops ◽  
Southwest Germany

Abstract The 3 September 1978, Swabian Jura (southwest Germany) earthquake (MWA = 5.7) was followed by a large number of aftershocks which have been recorded with a local network of five portable seismic stations. The seismic moments, fault radii, and the static stress drops have been determined from the SH displacement spectra using the Brune (1970) source model. The data set is consistent with the Gutenberg-Richter energy-magnitude relation. Below a Wood-Anderson magnitude of about 4, the corner frequencies increase only slowly with decreasing magnitudes. No corner frequency higher than 15 Hz has been observed in the magnitude range down to 0.8. Correspondingly, the high-frequency decay slopes show a strong increase when the corner frequencies are approaching the maximum frequency. This prevents the use of slope data for Q determinations. In terms of the Madariaga (1977) crack model, the data show a strong influence of source complexities on the smaller events.

A comparative seismic hazard study for Azerbaijan Province in Iran

1981 ◽  
Vol 71 (1) ◽  
pp. 335-362
Author(s):  
B. Rowshandel ◽  
S. Nemat-Nasser ◽  
R. B. Corotis
Keyword(s):  
Seismic Hazard ◽  
Point Source ◽  
Ground Motion ◽  
Line Source ◽  
Seismic Source ◽  
Source Model ◽  
Strike Slip ◽  
Area Source ◽  
Area Source Model ◽  
Line Source Model

abstract Different seismic source models are used to estimate regional seismic hazard. Commonly used point, line, and area seismic sources are considered in addition to a new method which is obtained by modifying the line source model to take into account the uncertainty associated with the exact location of the line (i.e., fault). The results are presented in terms of cumulative functions of peak ground acceleration for major sites in the Azerbaijan Province of northwest Iran. Iso-acceleration maps for two different return periods are also developed for each seismic source model and a comparison is made among the results of the models. The point source model is shown to be unrealistic when used to model large shocks (Ms > 6.5), which correspond to long ruptures. The model cannot incorporate the fault length, thus ignoring possible spatial migration of seismicity along the fault. In addition, the actual attenuation of ground motion departs considerably from that associated with point source assumption. The conventional line source model, while providing a good representation of vertical strike-slip faults, cannot accurately model the seismicity in other cases, such as reverse faults in general, and thrust (low angle reverse) faults in particular. Epicenters for these latter cases do not lie along a line, as they do in case of vertical strike-slip faults. The area source model is used for those cases where the distribution of earthquake epicenters in a region does not follow any identifiable geological fault pattern. The spatial migration of seismicity along an active fault during a given exposure time is of vital importance in seismic hazard analysis. An analysis based on an area source model corresponds to assuming this migration will be equal in all directions. The theory of plate tectonics, however, suggests an elongated narrow zone corresponding to each fault. A fault line model is developed which exhibits less sensitivity of near-field ground motion to precise fault location than the line source model. This model is referred to as the strip source model. According to this model, the seismicity on a fault is spatially distributed in a long and narrow zone along the margins of the corresponding plates or microplates, and decreases with distance from the fault on either side. It is believed that this kind of modeling closely represents the seismicity corresponding to interplate earthquakes, especially when the type of faulting is thrust. Uncertainties due to the location and orientation of faults will be considerable, particularly for the buried faults, and these uncertainties can be incorporated in the strip source model.

Two Empirical Double-Corner-Frequency Source Spectra and Their Physical Implications

2020 ◽  
Author(s):  
Chen Ji ◽  
Ralph J. Archuleta
Keyword(s):  
Standard Deviation ◽  
Ground Motion ◽  
Amplitude Spectrum ◽  
Stochastic Simulations ◽  
Corner Frequency ◽  
Sharp Change ◽  
Scaling Relation ◽  
Spectral Models ◽  
Self Similar ◽  
Scaled Energy

ABSTRACT We introduce double-corner-frequency (DCF) source spectral models JA19 and JA19_2S, which, in conjunction with a stochastic ground-motion model, can reproduce the mean peak ground acceleration (PGA) and mean peak ground velocity (PGV) of the Next Generation Attenuation-West 2 database for magnitudes 3.3–7.3. Their displacement amplitude spectrum remains constant for frequencies less than fc1, decays as f−1 between fc1 and fc2, and decays as f−2 for frequencies greater than fc2. The model JA19 is self-similar. Its two corner frequencies fc1 and fc2 scale with moment magnitude (M) as (1) log(fc1(M))=1.754−0.5M and (2) log(fc2(M))=3.250−0.5M. We find that relation (1) is consistent with the known self-similar scaling relations of the rupture duration (Td), in which Td=1/(πfc1). Relation (2) may reflect the scaling relation of the average rise time (TR), where TR∼0.8/(fc2). Stochastic simulations of ground motion using JA19 cannot reproduce the sharp change in magnitude dependence of PGA and PGV at M 5.3, suggesting a breakdown of self-similarity. The magnitude dependence of PGA and PGV and this change in slope is well explained by JA19_2S, which results from perturbing the fc1 scaling relationship in JA19. For JA19_2S: log(fc1(M))=1.474−0.415M for M≤5.3; log(fc1(M))=2.375−0.585M for M>5.3. The scaling relation for fc2 is unchanged. When fc1≪fc2, the scaled energy (ratio of radiated energy and seismic moment) scales with M0fc12fc2. The scaled energy of JA19 is 2.2×10−5, independent of magnitude. Because JA19_2S is not self-similar, its scaled energy is 2.2–4.7×10−5, increasing 2.2 times, when magnitude increases from 3.3 to 5.3, and, subsequently decreasing 2.2 times, as magnitude further increases from 5.3 to 7.3. Both agree with the global average (∼3×10−5) reported previously. Using our proposed empirical models, the standard deviation of average static stress drop from seismological studies can be significantly greater than the standard deviation of the stress parameter used to estimate PGA and PGV.

Simplified Dispersion Curves of Earthquake Love Wave for Rotational Seismic Motion Estimation

2014 ◽  
Vol 580-583 ◽  
pp. 1639-1644
Author(s):  
Yue Wei Liu ◽  
Hong Nan Li
Keyword(s):  
Ground Motion ◽  
Wave Velocity ◽  
Love Wave ◽  
Velocity Structure ◽  
Matrix Theory ◽  
Corner Frequency ◽  
Apparent Velocity ◽  
S Wave ◽  
Seismic Ground Motion ◽  
Seismic Motion

In the simulation of the rotational seismic ground motion, the apparent velocity of Love wave is always assumed to be equal to the S wave velocity of top layer of the site approximately, with the dispersion of surface wave not being fully considered. In this paper, the effect of the velocity structure to the Love wave dispersion is discussed based on the stiffness matrix theory. It shows that to assume the velocity to be equal to the S wave velocity of the top layer may greatly overestimate the low frequency rotational seismic motion. A simplified dispersion curve, is suggested for rotational seismic ground motion simulation. The shape of the bilinear curve is shaped by 3 parameters. They are the corner frequency, the minimum phase velocity and the velocity ratio. The parameters are affected by the velocity structure of the site.

Seismological Aspects of the 2003 Bam, Iran, Earthquake and Its Aftershock Analysis

2005 ◽  
Vol 21 (1_suppl) ◽  
pp. 101-112 ◽  
Author(s):  
M. Allamehzadeh ◽  
M. Dezvareh ◽  
A. M. Farahbod ◽  
D. Hatzfeld ◽  
M. Mokhtari ◽  
...  
Keyword(s):  
Pulse Duration ◽  
Source Model ◽  
Strike Slip ◽  
Body Waves ◽  
Corner Frequency ◽  
Vertical Alignment ◽  
Focal Mechanism Solutions ◽  
Source Radius ◽  
Fault Trace ◽  
Total Seismic Moment

The source mechanism derived from the inversion of long-period body waves revealed that the earthquake occurred on a north-south trending strike-slip fault with a thrust component. According to the source model estimated in this study, the 2003 Bam, Iran, earthquake was a multiple event formed by two subevents. The rupture following subevent one started at a depth of about 8 km. However, the depth of subevent two is about 10 km. The total seismic moment estimated from inversion processes is 8.34×1018Nm. The pulse duration of subevent one and subevent two was determined from source time function as 1.7 s and 0.8 s, respectively. Corner frequency and source radius have been calculated by using major pulse duration. The corner frequency and source radius are 0.187 Hz and 5.47 km, respectively. The aftershock events distributed along a 30 km north-south striking fault. The focal depths of aftershocks distribution show a nearly vertical alignment of aftershocks located between 6 and 20 km depth. The focal mechanism solutions of aftershocks indicate right-lateral strike-slip faulting on a north-south trending fault, parallel to the previously known Bam fault trace in the east of Bam.

The use of the coda for determination of the earthquake source spectrum

1978 ◽  
Vol 68 (4) ◽  
pp. 923-948 ◽  
Author(s):  
T. G. Rautian ◽  
V. I. Khalturin
Keyword(s):  
Frequency Band ◽  
Epicentral Distance ◽  
Source Parameters ◽  
Seismic Energy ◽  
The Body ◽  
Corner Frequency ◽  
Source Spectrum ◽  
Time Interval ◽  
S Wave ◽  
Absolute Amplitude

abstract We studied the spectral content and variations in time of the coda of seismic oscillations following the body and surface waves of local earthquakes. Within narrow frequency bands, the form of the envelope of the coda is remarkably stable—independent of epicenter (and therefore epicentral distance), depth of focus, and all other parameters of the source. Only the absolute amplitude of the coda differs from event to event. Similarly, the forms of the coda at two stations from the same earthquake overlap one another, differing only in absolute amplitude by a factor that is the same for all events. Hence given the form of the coda, its amplitude in any frequency band may be parameterized by one number—the amplitude at a certain time. Therefore, the spectrum of the coda as a function of time can be described as the product of two factors—one, independent of time, is dependent only on the source, and the other, reflecting the effects of the medium and the same for all sources, gives the time dependence for each frequency band. Segments of the envelopes with time can be matched by simple theories of scattering. Using the theoretical relationships, estimates of Q can be made and show that for any time interval, Q increases with frequency, approximately proportional to the square root of frequency. As longer elapsed times are considered, the estimates of Q increase, suggesting greater penetration of seismic energy into the higher Q parts of the Earth. The spectra of different events can be compared directly by comparing the spectra of the codas at the same elapsed time. Such a comparison reveals a wide variety of different source spectra. By using empirical relations among coda spectra, observed S-wave spectra, and theoretical constraints, an estimate of the spectrum radiated by the source can be calculated from the coda spectrum. Source parameters (seismic moment, corner frequency of the radiated spectrum, calculated stress drop, etc.) can be determined from coda spectra of events with many different moments and in different regions, with the same station. The results show several interesting features dependent on the seismic moments and on the regions in which the earthquakes occurred.

A statistical model for ground motion produced by earthquakes at local and regional distances

1990 ◽  
Vol 80 (6A) ◽  
pp. 1397-1417
Author(s):  
Gwo-Bin Ou ◽  
Robert B. Herrmann
Keyword(s):  
Ground Motion ◽  
Crustal Structure ◽  
Epicentral Distance ◽  
Amplitude Spectrum ◽  
Source Depth ◽  
S Wave ◽  
S Waves ◽  
Test Models ◽  
Peak Ground Motion ◽  
Random Process Theory

Abstract To adapt random process theory techniques for statistical estimation of peak ground motion to more realistic earth models, we constrain the parameters of duration, geometrical spreading, and spectral shape by modeling the main ground motion as being the result of major contributions by the direct S wave and supercritically reflected S waves. The results of our modeling are constrained to be consistent with values from full-wave synthetics for the test models. The combination of estimation theory and theoretical amplitude spectrum of the main ground motion within the ergodic window successfully predicts the mean peak vertical ground displacements, velocities, and accelerations of the 1982 Miramichi earthquakes in New Brunswick, Canada. In addition, upon considering the effects of source depth and crustal structure for the November 25, 1988, Saguenay earthquake (M = 5.8) in Québec, Canada, the predicted mean peak horizontal ground accelerations match the observed data very well. The effects of source depth and crustal structure on the peak ground motion are complicated for different source sizes and at different epicentral distance ranges.

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