The Mexico Earthquake of September 19, 1985—Relationships between Soil Conditions and Earthquake Ground Motions

1988 ◽  
Vol 4 (4) ◽  
pp. 687-729 ◽  
Author(s):  
H. B. Seed ◽  
M. P. Romo ◽  
J. I. Sun ◽  
A. Jaime ◽  
J. Lysmer
Keyword(s):  
Shear Wave ◽  
Mexico City ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ground Motions ◽  
Probabilistic Approach ◽  
General Nature ◽  
Soil Conditions ◽  
Ground Response ◽  
Local Soil

Comparisons are presented between the characteristics of ground motions at five sites underlain by clay at which ground motions were recorded in Mexico City in the earthquake of September 16, 1985 and for which analyses of ground response have been made, based on the measured properties of soils and the motions recorded on hard formations at the National University of Mexico. It is shown that the ground response in areas of Mexico City underlain by clay is extremely sensitive to small changes in the shear wave velocity of the clay and it is suggested that a probabilistic approach which allows for uncertainties in shear wave velocity measurements and in the characteristics of the motions on the hard formations is desirable to assess these effects. Based on the results of such an approach it is concluded that simple ground response analyses can provide very useful data for engineering assessments of the effects of local soil conditions on the characteristics of ground motions likely to develop at sites underlain by soft clays, and that the use of these procedures also provides a useful basis for estimating the general nature of the ground motions in the extensive heavy damage zone of Mexico City in the 1985 earthquake.

Seismic soil class map for Italy according to European and Italian codes map

2020 ◽  
Author(s):  
Giovanni Forte ◽  
Eugenio Chioccarelli ◽  
Melania De Falco ◽  
Pasquale Cito ◽  
Antonio Santo ◽  
...  
Keyword(s):  
Shear Wave ◽  
Ground Motion ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Large Scale ◽  
Soil Conditions ◽  
Site Classification ◽  
Soil Class ◽  
Topographic Slope ◽  
Geological Maps

<p>Soil conditions affect ground motion amplification. Thus, seismic site classification is a critical issue to predict ground motion parameters in the context of both probabilistic seismic hazard analysis and real-time generation of shaking maps. Especially on large areas, simplified procedures for estimating the seismic soil amplification can be advantageous. In order to account for these local effects, some proxies which account for the soil behaviour can be identified; e.g., the average shear-wave velocity of the upper 30 m (VS,30), or the equivalent shear-wave velocity from the depth of the seismic bedrock (VS,eq). <br>In this study, two maps of seismic shallow soil classification for Italy according to Eurocode 8 (EC08) and the new Italian Building Code (ItBC2018) are presented. The methodology from which the maps are derived is described in Forte et al. (2019) and accounts for two sources of information: site-specific measurements and large-scale geological maps. The soil maps are obtained via a four-step procedure: <br>(1) a database of about four-thousand shear-waves velocity (Vs) measurements coming from in-hole tests, surface geophysical tests and microtremors is built, covering (unevenly) the whole national territory; <br>(2) twenty geo-lithological complexes are identified from the available geological maps; <br>(3) the investigations are grouped as a function of the geo-lithological complex and the distribution of measured VS,30, VS,eq are derived;<br>(4) medians and standard deviations of such distributions are assumed to be representative of the corresponding complexes that are consequently associated to soil classes. <br>The EC08 soil class map and the available database of Vs measurements were compared with the seismic soil map provided by the USGS based on a topographic slope-proxy (Allen and Wald, 2007). The latter is obtained by the correlation between topographic slope and VS,30, assuming morphometrical characteristics of the terrain as representative of the lithology. The slope-based method appears less reliable than the proposed approach, because its predictions resulted in a slight but systematic overestimation of the measured soil classes. Therefore, the proposed map can be more suitable for large-scale seismic risk studies, despite it is not a substitute of seismic microzonation and local site response analyses.<br>To make the results of the study available, a stand-alone software “SSC-Italy” has been developed and is freely available at http://wpage. unina.it/iuniervo/SSC-Italy.zip. </p>

Strong ground motions recorded during earthquakes of May the 11th and 19th, 1962 in Mexico City

1964 ◽  
Vol 54 (1) ◽  
pp. 209-231
Author(s):  
Leonardo Zeevaert
Keyword(s):  
Mexico City ◽  
Ground Motions ◽  
Soft Clay ◽  
Response Spectra ◽  
The Other ◽  
Soil Conditions ◽  
Strong Ground Motions ◽  
Multistory Building ◽  
Local Soil ◽  
Strong Ground

abstract The ground accelerations during the earthquakes of May 11 and 19, 1962 were recorded in Mexico City on a soft clay bed that was formerly the floor of an old lake. Records were obtained from two accelerometers, one instrument was located in the basement of a multistory building and the other was located in a nearby park. Response spectra of the ground motions are presented and analysis is made of the local soil conditions with the view to explaining the characteristics of the spectrums.

Basin and Site Effects in the U.S. Pacific Northwest Estimated from Small-Magnitude Earthquakes

2021 ◽  
Author(s):  
John M. Rekoske ◽  
Morgan P. Moschetti ◽  
Eric M. Thompson
Keyword(s):  
Shear Wave ◽  
Pacific Northwest ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Site Effects ◽  
Site Response ◽  
Ground Motions ◽  
Sedimentary Basins ◽  
Small Magnitude ◽  
The U.S

ABSTRACT Earthquake hazards in the U.S. Pacific Northwest (PNW) are increased by the presence of deep sedimentary basins that amplify and prolong ground shaking. To better understand basin and site effects on ground motions, we compile a database of recordings from crustal and intraslab earthquakes. We process 8028 records with magnitudes from 3.5 to 6.8 and hypocentral depths up to 62 km to compute Fourier amplitude spectra of ground acceleration for frequencies of 0–20 Hz. We compute residuals relative to the Bayless and Abrahamson (2019; hereafter, BA18) ground-motion model and perform a series of linear, crossed, mixed-effects regressions. In addition to estimating the bias, event, and site terms, we incorporate groupings for broad regionalized site response in three different regions (Seattle basin, Puget Lowland, non-Puget Lowland), for effects from seismotectonic regime (crustal and intraslab sources), and for interactions between the regions and seismotectonic regimes. We find that the scaling of site response with respect to VS30 (time-averaged shear-wave velocity from the surface to a depth of 30 m) and to basin depth indicators Z1.0 and Z2.5 (depths to the 1.0 and 2.5 km/s shear-wave velocity horizons) is generally consistent with BA18; however, the region terms display strong spatial amplification patterns. For frequencies less than 5 Hz, the Seattle basin amplifies ground motions up to a factor of four, relative to the non-Puget Lowland, with a maximum amplification around near 0.5 Hz. Sites in the Puget Lowland amplify low frequencies up to a factor of 2.5. At higher frequencies (f>5  Hz), the Puget Lowland and Seattle basin show regional deamplification of ground motions, with the smallest average amplification factor of 0.65 occurring at 10.0 Hz. Although we observe slight differences in the seismotectonic regime terms, we find that the region terms are significantly more important for modeling earthquake hazard in the PNW.

Predicting Wave Propagation Through Inhomogeneous Soils Using a Finite-Element Model Incorporating Perfectly-Matched Layers

2015 ◽  
Author(s):  
Simon Jones
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Element Model ◽  
Perfectly Matched Layer ◽  
Surface Velocity ◽  
Perfectly Matched Layers ◽  
Local Soil

A 2D, plane-strain, finite element model, with perfectly-matched layer elements acting as absorbing boundaries, is used to investigate the effect of soil inhomogeneity on resultant surface vibration. The stiffness and mass matrices for the perfectly-matched layer element is derived and included for reference. Stochastic variability of the soil’s shear wave velocity is introduced using a K-L expansion; the shear wave velocity is assumed to have a log-normal distribution and a modified exponential co-variance kernel. Results suggest that local soil inhomogeneity can significantly affect surface velocity predictions; 90% confidence intervals showing 7dB averages and peak values up to 11dB are computed. This is a significant source of uncertainty and should be considered when using predictions from models assuming homogeneous soil properties.

Impact of spatial variability of shear wave velocity on the lagged coherency of synthetic surface ground motions

2021 ◽  
Vol 145 ◽  
pp. 106689
Author(s):  
E. El Haber ◽  
C. Cornou ◽  
D. Jongmans ◽  
F. Lopez-Caballero ◽  
D. Youssef Abdelmassih ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ground Motions
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