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.

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.

Thin-bed prestack spectral inversion

Geophysics ◽  
2009 ◽  
Vol 74 (4) ◽  
pp. R49-R57 ◽  
Author(s):  
J. Germán Rubino ◽  
Danilo Velis
Keyword(s):  
Time Window ◽  
A Priori ◽  
Amplitude Spectrum ◽  
Wavelet Spectrum ◽  
Model Parameters ◽  
Data Sets ◽  
S Wave ◽  
P Waves ◽  
S Waves ◽  
Zero Offset

Prestack seismic data has been used in a new method to fully determine thin-bed properties, including the estimation of its thickness, P- and S-wave velocities, and density. The approach requires neither phase information nor normal-moveout (NMO) corrections, and assumes that the prestack seismic response of the thin layer can be isolated using an offset-dependent time window. We obtained the amplitude-versus-angle (AVA) response of the thin bed considering converted P-waves, S-waves, and all the associated multiples. We carried out the estimation of the thin-bed parameters in the frequency (amplitude spectrum) domain using simulated annealing. In contrast to using zero-offset data, the use of AVA data contributes to increase the robustness of this inverse problem under noisy conditions, as well as to significantly reduce its inherent nonuniqueness. To further reduce the nonuniqueness, and as a means to incorporate a priori geologic or geophysical information (e.g., well-log data), we imposed appropriate bounding constraints to the parameters of the media lying above and below the thin bed, which need not be known accurately. We tested the method by inverting noisy synthetic gathers corresponding to simple wedge models. In addition, we stochastically estimated the uncertainty of the solutions by inverting different data sets that share the same model parameters but are contaminated with different noise realizations. The results suggest that thin beds can be characterized fully with a moderate to high degree of confidence below tuning, even when using an approximate wavelet spectrum.

Empirical Spatial Coherency Functions for Application to Soil-Structure Interaction Analyses

1991 ◽  
Vol 7 (1) ◽  
pp. 1-27 ◽  
Author(s):  
N. A. Abrahamson ◽  
J. F. Schneider ◽  
J. C. Stepp
Keyword(s):  
Ground Motion ◽  
Soil Structure ◽  
Epicentral Distance ◽  
Strong Motion ◽  
Soil Structure Interaction ◽  
High Frequencies ◽  
S Waves ◽  
Structure Interaction ◽  
Strong Ground ◽  
Spatial Coherency

The spatial coherency of strong ground motion from fifteen earthquakes recorded by the Lotung LSST strong motion array is analyzed. The earthquakes range in magnitude from 3.7 to 7.8 and in epicentral distance from 5 to 80 km. In all, a total of 533 station pairs are used with station separations ranging from 6 to 85 meters. Empirical coherency functions for the horizontal component S-waves appropriate for use in engineering analyses are derived from these data. The derived coherency functions are applicable to all frequencies and to separation distances up to 100 m. For these short station separations, the coherency decreases much faster with increasing frequency than with increasing station separation. The computed coherencies indicate that at high frequencies (>10 Hz) over 25 percent of the power of the ground motion is random for station separations greater than 30 m.

scholarly journals Modelling of pulse-like velocity ground motion during the 2018 Mw 6.3 Hualien earthquake, Taiwan

2020 ◽  
Vol 223 (1) ◽  
pp. 348-365 ◽  
Author(s):  
Yen-Yu Lin ◽  
Hiroo Kanamori ◽  
Zhongwen Zhan ◽  
Kuo-Fong Ma ◽  
Te-Yang Yeh
Keyword(s):  
Ground Motion ◽  
Site Effects ◽  
Strong Motion ◽  
S Wave ◽  
Finite Fault ◽  
Peak Ground Motion ◽  
Large Velocity ◽  
Reversed Polarity ◽  
Local Slip ◽  
Strong Motion Network

SUMMARY The 2018 February 6 Mw 6.3 Hualien earthquake caused severe localized damage in Hualien City, located 20 km away from the epicentre. The damage was due to strong (>70 cm s−1) and sharp (duration ∼2.5 s) velocity pulses. The observed peak ground-motion velocity in Hualien City symmetrically decays with distance from the nearby Milun fault. Waveforms observed on the opposite sides of the fault show reversed polarity on the vertical and N–S components while the E–W component is almost identical. None of the published finite-fault slip models can explain the spatially highly localized large velocity pulses. In this study, we show that an Mw 5.9 strike-slip subevent on the Milun fault at 2.5 km depth, rupturing from north to south at ∼0.9Vs speed, combined with site effects caused by surficial layers with low S-wave speed, can explain the velocity pulses observed at the dense strong-motion network stations. This subevent contributes only 25 per cent of the total moment of the 2018 Hualien earthquake, suggesting that a small local slip patch near a metropolis can dominate the local hazard. Our result strongly suggests that seismic hazard assessments should consider large ground-motion variabilities caused by directivity and site effects, as observed in the 2018 Hualien earthquake.

Crust, mantle and core structure of Mars from InSight seismic data

2021 ◽  
Author(s):  
Amir Khan ◽  
Keyword(s):  
Epicentral Distance ◽  
Body Wave ◽  
Low Frequency ◽  
Distance Estimation ◽  
Velocity Model ◽  
Interior Structure ◽  
S Wave ◽  
S Waves ◽  
The Core ◽  
Radial Profiles

<p>With the deployment of a seismometer on the surface of Mars as part of NASA’s InSight mission,<br />the Seismic Experiment for Interior Structure (SEIS) has been collecting continuous data since early 2019.<br />The primary goal of InSight is to improve our understanding of the internal structure and dynamics of Mars, in<br />particular crust, mantle, and core. Here we describe constraints on the structure of the mantle of Mars based<br />on inversion of seismic body wave arrivals from a number of low-frequency marsquakes.</p> <p>We consider 8 of the largest (moment magnitude is estimated to be between 3 and 4) low-frequency events with<br />dominant energy below 1 Hz for which P- and S-waves are identifiable, enabling epicentral distance estimation.<br />The 8 events occur in the distance range 25-75 degrees. Body wave arrivals that include the main P- and S-waves,<br />surface reflections (PP, PPP, SS, SSS), and core reflections (ScS) are picked using a set of complimentary methods<br />that allows to check for consistency. The resultant set of differential travel times (PP-P, PPP-P, SS-S,...) are<br />subsequently inverted for radial profiles of seismic P- and S-wave velocity, core size and mean density, and epicentral<br />location of the events. To determine interior structure, we rely on independent methods as a means of assessing the<br />robustness of the results.</p> <p>We present a radial velocity model for the upper mantle of Mars, with implications for the thermo-chemical evolution<br />of the planet that match a cooling, differentiated body, and a thick lithosphere. Based on the location of the events,<br />we are able to constrain structure to the core-mantle-boundary, including the size of the core and its mean<br />density that point to large liquid and relatively light core, implying a significant complement of light alloying<br />elements. Our estimate of the average crustal thickness as seen by all events is compatible with the local crustal<br />thickness at the InSight landing determined from observations of converted phases.</p>

Observations in support of Rg scattering as a source for explosion S waves: Regional and local recordings of the 1997 Kazakhstan depth of burial experiment

1999 ◽  
Vol 89 (2) ◽  
pp. 544-549 ◽  
Author(s):  
Stephen C. Myers ◽  
William R. Walter ◽  
Kevin Mayeda ◽  
Lewis Glenn
Keyword(s):  
Test Site ◽  
Field Analysis ◽  
Significant Shift ◽  
Source Depth ◽  
Amplitude Ratios ◽  
Physical Processes ◽  
S Wave ◽  
S Waves ◽  
Chemical Explosions ◽  
Depth Of Burial

Abstract In August and September of 1997, three 25-ton chemical explosions were detonated at nominal depths of 550, 300, and 50 m in boreholes at the former Soviet test site at Balapan, Kazakhstan. One objective of this experiment was to evaluate the effect of differing source depth on the regional wave field. Analysis of regional seismic phases lead to the observation that regional P/S wave amplitude ratios in the 1- to 5-Hz band increase as a function of source depth. However, at frequencies greater than about 5 Hz, the relative amplitudes of P and S waves remain approximately constant for the differing depth shots. Similarly, regional coda spectra are amplified in the 1- to 5-Hz band for the shallow shots. At local distances, Rg is the dominant seismic phase, with peak amplitudes in the 0.7- to 5-Hz range, and Rg is strongest for the shallower shots. Within the short distance spanned by the local stations (<20 km), Rg is rapidly attenuated, and the attenuation is accompanied by a significant shift in peak amplitude toward lower frequency. At regional distances, Rg is below the noise level. The coincident frequency band in which local Rg rapidly loses energy and regional S phases are amplified points toward Rg scattering as the dominant mechanism causing the discrepancies between P/S amplitude ratios in this study. These observations are particularly relevant to the understanding of physical processes affecting regional P/S discriminants and may lead to improvements in discriminant methods.

The effect of the earth's surface on the S wave particle motion

1961 ◽  
Vol 51 (2) ◽  
pp. 237-246
Author(s):  
Otto Nuttli
Keyword(s):  
Ground Motion ◽  
Particle Motion ◽  
Plane Surface ◽  
Epicentral Distance ◽  
Wave Length ◽  
Three Dimensional ◽  
S Wave ◽  
Time Curve ◽  
Three Components

Abstract This paper is concerned with the determination of the particle motion of the earth's surface due to the incidence of a plane S wave of arbitrary polarization and incidence angles. It is assumed that the earth's surface may be represented by a plane surface. For angles of incidence less than sin-1(b0/a0, where a0 and b0 are the P and S wave velocities at the earth's surface, all three components of ground motion will be in phase, and the resultant motion is linear. For angles of incidence greater than sin-1(b0/a0), all three components of ground motion will in general be out of phase, with the resultant motion describing some three-dimensional figure. The epicentral distance at which the motion changes from linear to non-linear depends upon the wave length of the S wave and the slope of the travel time curve at that distance.

The High-Frequency Decay Slope of Spectra (Kappa) for M≥3.5 Earthquakes on Rock Sites in Eastern and Western Canada

2020 ◽  
Vol 110 (2) ◽  
pp. 471-488 ◽  
Author(s):  
Samantha M. Palmer ◽  
Gail M. Atkinson
Keyword(s):  
Ground Motion ◽  
Classical Method ◽  
Vertical Component ◽  
Western Canada ◽  
S Wave ◽  
Motion Modeling ◽  
Eastern Canada ◽  
General Observation ◽  
Anelastic Attenuation ◽  
Two Parameters

ABSTRACT Spectral decay of ground-motion amplitudes at high frequencies is primarily influenced by two parameters: site-related kappa (κ0) and regional Q (quality factor, inversely proportional to anelastic attenuation). We examine kappa and apparent Q-values (Qa) for M≥3.5 earthquakes recorded at seismograph stations on rock sites in eastern and western Canada. Our database contains 20 earthquakes recorded on nine stations in eastern Canada and 404 earthquakes recorded on eight stations in western Canada, resulting in 105 and 865 Fourier amplitude spectra, respectively. We apply two different methods: (1) a modified version of the classical S-wave acceleration method; and (2) a new stacking method that is consistent with the use of kappa in ground-motion modeling. The results are robust with respect to the method used and also with respect to the frequency band selected, which ranges from 9 to 38 Hz depending on the region, event, and method. Kappa values obtained from the classical method are consistent with those of the stacked method, but the stacked method provides a lower uncertainty. A general observation is that kappa is usually larger, and apparent Q is smaller, for the horizontal component in comparison to the vertical component. We determine an average regional κ0=7  ms (horizontal) and 0 ms (vertical) for rock sites in eastern Canada; we obtain κ0=19  ms (horizontal) and 14 ms (vertical) for rock sites in western Canada. We note that kappa measurements are quite sensitive to details of data selection criteria and methodology, and may be significantly influenced by site effects, resulting in large site-to-site variability.

scholarly journals Responses of dipole-source reflected shear waves in acoustically slow formations

2019 ◽  
Author(s):  
Hao Wang ◽  
Ning Li ◽  
Caizhi Wang ◽  
Hongliang Wu ◽  
Peng Liu ◽  
...  
Keyword(s):  
Finite Difference Time Domain ◽  
Dipole Source ◽  
Sh Wave ◽  
S Wave ◽  
High Fracture ◽  
S Waves ◽  
Angle Fracture ◽  
Dip Angle ◽  
Difference Time

Abstract In the process of dipole-source acoustic far-detection logging, the azimuth of the fracture outside the borehole can be determined with the assumption that the SH–SH wave is stronger than the SV–SV wave. However, in slow formations, the considerable borehole modulation highly complicates the dipole-source radiation of SH and SV waves. A 3D finite-difference time-domain method is used to investigate the responses of the dipole-source reflected shear wave (S–S) in slow formations and explain the relationships between the azimuth characteristics of the S–S wave and the source–receiver offset and the dip angle of the fracture outside the borehole. Results indicate that the SH–SH and SV–SV waves cannot be effectively distinguished by amplitude at some offset ranges under low- and high-fracture dip angle conditions, and the offset ranges are related to formation properties and fracture dip angle. In these cases, the fracture azimuth determined by the amplitude of the S–S wave not only has a $180^\circ $ uncertainty but may also have a $90^\circ $ difference from the actual value. Under these situations, the P–P, S–P and S–S waves can be combined to solve the problem of the $90^\circ $ difference in the azimuth determination of fractures outside the borehole, especially for a low-dip-angle fracture.

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