Stochastic field analyses of the site amplification factors based on observed and inversely analyzed real strong ground motion in Japan

<p>The Mw 6.9 earthquake that took place offshore between the Greek island of Samos and Turkey&#8217;s &#304;zmir province on 30 October 2020 came hardly as a surprise. Due to the extensional tectonic regime of the Aegean and high deformation rates, earthquakes of similar size frequently occur in the Aegean Sea on fault segments close to the shores of Turkey, affecting the settlements on mainland Turkey and on the Greek Islands. Samos-Sigacik earthquake had a normal faulting mechanism. It was recorded by the strong motion networks in Turkey and Greece. Although expected, the earthquake was an&#160; outstanding event in the sense of&#160; highly localized, significant levels of building damage as a result of amplified ground motion levels. This presentation is an overview of strong ground motion characteristics of this important event both regionally and locally. Mainshock records suggest that local site effects, enhanced by basin effects could be responsible for structural damage in central Izmir, the third largest city of Turkey located at 60-70 km epicentral distance. We installed a seven-station network in Bayrakl&#305; and Kar&#351;&#305;yaka districts of &#304;zmir within three days of the mainshock in search of site and basin effects.&#160; Through analysis of recorded aftershocks we explore the amplification characeristics of soils in the two aforementioned districts&#160; and try to understand the role basin effects might have played in the resulting ground motion levels and consequently damage.&#160;</p>

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The effect of quaternary alluvium on strong ground motion in the Coyote Lake, California, earthquake of 1979

Bulletin of the Seismological Society of America ◽

10.1785/bssa0710041333 ◽

1981 ◽

Vol 71 (4) ◽

pp. 1333-1349 ◽

Cited By ~ 2

Author(s):

William B. Joyner ◽

Richard E. Warrick ◽

Thomas E. Fumal

Keyword(s):

Ground Motion ◽

Strong Ground Motion ◽

Site Amplification ◽

Horizontal Velocity ◽

Surface Velocity ◽

Near Surface ◽

Soil Response ◽

A Site ◽

Strong Ground ◽

Good Agreement

abstract The effect of alluvium on strong ground motion can be seen by comparing two strong-motion records of the Coyote Lake, California, earthquake of 6 August 1979 (ML = 5.9). One record at a site on Franciscan bedrock had a peak horizontal acceleration of 0.13 g and a peak horizontal velocity of 10 cm/sec. The other, at a site 2 km distant on 180 meters of Quaternary alluvium overlying Franciscan, had values of 0.26 g and 32 cm/sec, amplifications by factors of 2 and 3. Horizontal motions computed at the alluvial site for a linear plane-layered model based on measured P and S velocities show reasonably good agreement in shape with the observed motions, but the observed peak amplitudes are greater by a factor of about 1.25 in acceleration and 1.8 in velocity. About 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance; the remainder may represent focusing by refraction at a bedrock surface concave upward. There is no clear evidence of nonlinear soil response. Fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model. In particular, the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value, indicating that no significant nonlinearity occurs in the secant shear modulus. Computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0.5 to 1.0 or greater. The data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections, and more the simple effect of the low near-surface velocity. Application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear-wave velocity.

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Turkey-Adjusted NGA-W1 Horizontal Ground Motion Prediction Models

Earthquake Spectra ◽

10.1193/022714eqs034m ◽

2016 ◽

Vol 32 (1) ◽

pp. 75-100 ◽

Cited By ~ 14

Author(s):

Zeynep Gülerce ◽

Bahadır Kargoığlu ◽

Norman A. Abrahamson

Keyword(s):

Ground Motion ◽

Strong Ground Motion ◽

Prediction Models ◽

Ground Motions ◽

Site Amplification ◽

Motion Prediction ◽

Ground Motion Prediction ◽

Data Set ◽

Horizontal Ground Motion ◽

Strong Ground

The objective of this paper is to evaluate the differences between the Next Generation Attenuation: West-1 (NGA-W1) ground motion prediction models (GMPEs) and the Turkish strong ground motion data set and to modify the required pieces of the NGA-W1 models for applicability in Turkey. A comparison data set is compiled by including strong motions from earthquakes that occurred in Turkey and earthquake metadata of ground motions consistent with the NGA-W1 database. Random-effects regression is employed and plots of the residuals are used to evaluate the differences in magnitude, distance, and site amplification scaling. Incompatibilities between the NGA-W1 GMPEs and Turkish data set in small-to-moderate magnitude, large distance, and site effects scaling are encountered. The NGA-W1 GMPEs are modified for the misfit between the actual ground motions and the model predictions using adjustments functions. Turkey-adjusted NGA-W1 models are compatible with the regional strong ground motion characteristics and preserve the well-constrained features of the global models.

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