Regional propagation characteristics and source parameters of earthquakes in northeastern North America

1994 ◽  
Vol 84 (1) ◽  
pp. 1-15 ◽  
Author(s):  
John Boatwright
Keyword(s):  
Site Response ◽  
Source Parameters ◽  
Low Frequency ◽  
Response Spectra ◽  
Spectral Shape ◽  
Propagation Characteristics ◽  
S Wave ◽  
Data Set ◽  
Wave Trains ◽  
Source Site

Abstract The vertical components of the S wave trains recorded on the Eastern Canadian Telemetered Network (ECTN) from 1980 through 1990 have been spectrally analyzed for source, site, and propagation characteristics. The data set comprises some 1033 recordings of 97 earthquakes whose magnitudes range from M ≈ 3 to 6. The epicentral distances range from 15 to 1000 km, with most of the data set recorded at distances from 200 to 800 km. The recorded S wave trains contain the phases S, SmS, Sn, and Lg and are sampled using windows that increase with distance; the acceleration spectra were analyzed from 1.0 to 10 Hz. To separate the source, site, and propagation characteristics, an inversion for the earthquake corner frequencies, low-frequency levels, and average attenuation parameters is alternated with a regression of residuals onto the set of stations and a grid of 14 distances ranging from 25 to 1000 km. The iteration between these two parts of the inversion converges in about 60 steps. The average attenuation parameters obtained from the inversion were Q = 1997 ± 10 and γ = 0.998 ± 0.003. The most pronounced variation from this average attenuation is a marked deamplification of more than a factor of 2 at 63 km and 2 Hz, which shallows with increasing frequency and increasing distance out to 200 km. The site-response spectra obtained for the ECTN stations are generally flat. The source spectral shape assumed in this inversion provides an adequate spectral model for the smaller events (Mo < 3 × 1021 dyne-cm) in the data set, whose Brune stress drops range from 5 to 150 bars. For the five events in the data set with Mo ≧ 1023 dyne-cm, however, the source spectra obtained by regressing the residuals suggest that an ω2 spectrum is an inadequate model for the spectral shape. In particular, the corner frequencies for most of these large events appear to be split, so that the spectra exhibit an intermediate behavior (where |ü(ω)| is roughly proportional to ω).

A site effect study in Acapulco, Guerrero, Mexico: Comparison of results from strong-motion and microtremor data

1992 ◽  
Vol 82 (2) ◽  
pp. 642-659 ◽  
Author(s):  
Carlos Gutierrez ◽  
Shri Krishna Singh
Keyword(s):  
Seismic Waves ◽  
Site Response ◽  
Nonlinear Behavior ◽  
Strong Motion ◽  
Site Effect ◽  
Seismic Gap ◽  
S Wave ◽  
Data Set ◽  
S Waves ◽  
The City

Abstract The city of Acapulco is located near or above the mature seismic gap of Guerrero along the Mexican subduction zone. With the purpose of studying the character of strong ground motion on soft sites, four digital accelerographs have been installed in the city on such sites. These instruments have been in operation since 1988. Two additional instruments, part of the Guerrero Accelerograph Array, are located on hard sites in the area. One of these, VNTA, has been in operation since 1985 and the other, ACAN, since 1989. These stations have recorded several earthquakes. We use data from eight events (4.2 ≤ M ≤ 6.9) to study spectral amplification of seismic waves at the soft sites with respect to VNTA. The S waves are amplified by a factor of 6 to 25 at the soft sites in a fairly broad range of frequencies; both the amplification and the frequency band over which it occurs depend upon the site. Although the largest earthquake in our data set (M = 6.9) gave rise to a peak horizontal acceleration exceeding 0.3 g at one of the soft sites, no clear evidence of nonlinear behavior of the subsoil is found. Spectral amplifications of S-wave coda are very similar to those of S waves. We also measured microtremors at the strong-motion sites. The microtremor spectra were interpreted, using reasonable assumptions, to test the feasibility of this technique in reproducing the spectral amplifications observed during earthquakes. Our results show that only a rough estimate of site response can be obtained from this technique, at least in Acapulco; caution is warranted in its use elsewhere.

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>

EURO-SEISTEST strong-motion array near Thessaloniki, Northern Greece: A study of site effects

1998 ◽  
Vol 88 (3) ◽  
pp. 862-873
Author(s):  
P. P. Dimitriu ◽  
Ch. A. Papaioannou ◽  
N. P. Theodulidis
Keyword(s):  
Wave Propagation ◽  
Time Window ◽  
Site Response ◽  
Strong Motion ◽  
Spectral Ratio ◽  
Response Spectra ◽  
Response Assessment ◽  
Northern Greece ◽  
Data Set ◽  
Propagation Models

Abstract The effects of local geology on the characteristics of strong ground motion have been, and continue to be, a field of active research. Despite the considerable efforts made so far, there are still several unresolved and controversial issues remaining. In particular, debates still continue over the limits of applicability of one-dimensional (1D) wave-propagation models. There are also unresolved questions related to the implementation and reliability of site-response estimation techniques such as the standard spectral ratio (SSR) and the horizontal-to-vertical spectral ratio (HVSR). This study addresses these issues on the basis of data from the EURO-SEISTEST strong-motion array at Volvi, near Thessaloniki, Greece. The data set used consists of accelerograms of 32 earthquakes, almost exclusively local, covering a magnitude range from ML 2.0 to 6.1. The range of recorded accelerations is 0.001 − 0.042 g. We implement two 1D wave-propagation models (the Haskell-Thompson matrix method and Kennett's reflectivity-coefficient method) and the HVSR site-response assessment technique. We test the applicability of the 1D models in a basin environment. We use both Fourier-amplitude and response spectra to compute HVSR and investigate how HVSR is influenced by the choice of the time window and smoothing procedure. We found the HVSR technique and 1D SH-wave modeling to perform reasonably well in a sediment-valley environment (the modeling was performed for a site in the center of the valley).

Seismic site response in the greater Vancouver, British Columbia, area: spectral ratios from moderate earthquakes

1999 ◽  
Vol 36 (2) ◽  
pp. 195-209 ◽  
Author(s):  
John F Cassidy ◽  
Garry C Rogers
Keyword(s):  
Site Response ◽  
Strong Motion ◽  
River Delta ◽  
Data Sets ◽  
Fraser River ◽  
Spectral Ratios ◽  
Data Set ◽  
Seismic Site Response ◽  
Fraser River Delta ◽  
S Period

Three-component, digital recordings of two recent moderate earthquakes provide valuable new insight into the response to seismic shaking in the greater Vancouver area, particularly on the Fraser River delta. The 1996 M = 5.1 Duvall, Washington, earthquake (180 km southeast of Vancouver) triggered strong-motion seismographs at seven sites and the 1997 M = 4.3 Georgia Strait earthquake (37 km west of Vancouver) triggered instruments at 13 sites in the greater Vancouver area. The latter data set is especially important because it contains the first three-component recordings made on bedrock in greater Vancouver. Both data sets represent weak ground motion, with peak horizontal accelerations of 0.5-1.5% gravity (g) for the Duvall earthquake, and 0.2-2.4% g for the Georgia Strait earthquake. Using the method of spectral ratios, we estimate the site response for each of the strong-motion instrument soil sites. On the Fraser River delta amplification is observed over a relatively narrow frequency range of 1.5-4 Hz (0.25-0.67 s period), with peak amplification of 4-10 (relative to competent bedrock) for the thick soil delta centre sites, and about 7-11 for the delta edge sites. Relative to firm soil, the peak amplification ranges from 2 to 5 for the thick soil delta centre sites, and 2 to 6 for the delta edge sites. At higher frequencies, little or no amplification, and in many cases slight attenuation, is observed.Key words: seismic site response, Fraser delta, earthquakes.

Strain to Ground Motion Conversion of DAS Data for Earthquake Magnitude and Stress Drop Determination

2021 ◽  
Author(s):  
Itzhak Lior ◽  
Anthony Sladen ◽  
Diego Mercerat ◽  
Jean-Paul Ampuero ◽  
Diane Rivet ◽  
...  
Keyword(s):  
Early Warning ◽  
Stress Drop ◽  
Source Parameters ◽  
Simulated Data ◽  
Earthquake Early Warning ◽  
Body Waves ◽  
Ocean Bottom ◽  
Correlated Noise ◽  
S Wave ◽  
Earthquake Source Parameters

<p>The use of Distributed Acoustic Sensing (DAS) presents unique advantages for earthquake monitoring compared with standard seismic networks: spatially dense measurements adapted for harsh environments and designed for remote operation. However, the ability to determine earthquake source parameters using DAS is yet to be fully established. In particular, resolving the magnitude and stress drop, is a fundamental objective for seismic monitoring and earthquake early warning. To apply existing methods for source parameter estimation to DAS signals, they must first be converted from strain to ground motions. This conversion can be achieved using the waves’ apparent phase velocity, which varies for different seismic phases ranging from fast body-waves to slow surface- and scattered-waves. To facilitate this conversion and improve its reliability, an algorithm for slowness determination is presented, based on the local slant-stack transform. This approach yields a unique slowness value at each time instance of a DAS time-series. The ability to convert strain-rate signals to ground accelerations is validated using simulated data and applied to several earthquakes recorded by dark fibers of three ocean-bottom telecommunication cables in the Mediterranean Sea. The conversion emphasizes fast body-waves compared to slow scattered-waves and ambient noise, and is robust even in the presence of correlated noise and varying wave propagation directions. Good agreement is found between source parameters determined using converted DAS waveforms and on-land seismometers for both P- and S-wave records. The demonstrated ability to resolve source parameters using P-waves on horizontal ocean-bottom fibers is key for the implementation of DAS based earthquake early warning, which will significantly improve hazard mitigation capabilities for offshore and tsunami earthquakes.</p>

Retrieval of source-extent parameters and the interpretation of corner frequency

1983 ◽  
Vol 73 (6A) ◽  
pp. 1499-1511
Author(s):  
Paul Silver
Keyword(s):  
Body Wave ◽  
Amplitude Spectrum ◽  
Low Frequency ◽  
P Wave ◽  
Corner Frequency ◽  
S Wave ◽  
Dislocation Source ◽  
Statistical Measures ◽  
Dislocation Models ◽  
Planar Dislocation

Abstract A method is proposed for retrieving source-extent parameters from far-field body-wave data. At low frequency, the normalized P- or S-wave displacement amplitude spectrum can be approximated by |Ω^(r^,ω)| = 1 − τ2(r^)ω2/2 where r^ specifies a point on the focal sphere. For planar dislocation sources, τ2(r^) is linearly related to statistical measures of source dimension, source duration, and directivity. τ2(r^) can be measured as the curvature of |Ω^(r^,ω)| at ω = 0 or the variance of the pulse Ω^(r^,t). The quantity ωc=2τ−1(r^) is contrasted with the traditional corner frequency ω0, defined as the frequency at the intersection of the low- and high-frequency trends of |Ω^(r^,ω)|. For dislocation models without directivity, ωc(P) ≧ ωc(S) for any r^. A mean corner frequency defined by averaging τ2(r^) over the focal sphere, ω¯c=2<τ2(r^)>−1/2, satisfies ωc(P) > ωc(S) for any dislocation source. This behavior is not shared by ω0. It is shown that ω0 is most sensitive to critical times in the rupture history of the source, whereas ωc is determined by the basic parameters of source extent. Evidence is presented that ωc is the corner frequency measured on actual seismograms. Thus, the commonly observed corner frequency shift (P-wave corner greater than the S-wave corner), now viewed as a shift in ωc is simply a result of spatial finiteness and is expected to be a property of any dislocation source. As a result, the shift cannot be used as a criterion for rejecting particular dislocation models.

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