Francisco J. Chávez‐García

Universidad Nacional Autónoma de México

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Dimitrios Raptakis

Aristotle University of Thessaloniki

Kyriazis Pitilakis

Aristotle University of Thessaloniki

Konstantia Makra

Institute of Engineering Seismology and Earthquake Engineering

Pierre‐Yves Bard

Centre National de la Recherche Scientifique

Orhan Polat

Dokuz Eylül University

Maria Manakou

Aristotle University of Thessaloniki

Emre Mulumulu

Dokuz Eylül University

Miguel Rodríguez

Universidad Nacional Autónoma de México

W. R. Stephenson

GNS Science

Francisco J. Sánchez‐Sesma

Universidad Nacional Autónoma de México

Cooperative Institutions

Universidad Nacional Autónoma de México

Université Grenoble Alpes

Centre National de la Recherche Scientifique

Université Gustave Eiffel

Institut des Sciences de la Terre

Aristotle University of Thessaloniki

Dokuz Eylül University

Institut de Recherche pour le Développement

Université Savoie Mont Blanc

University of Quindío

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Topographic site effects and HVSR. A comparison between observations and theory

Bulletin of the Seismological Society of America (1996)

Francisco J. Chávez‐García Luis Ramón Cázares Sánchez D. Hatzfeld

Abstract We present a comparison between observed and predicted amplification on a topographic feature. Our data come from an ad hoc experiment carried out during the summer of 1989, in Epire (Northern Greece). Ten digital, autonomous, three-component stations recorded a total of 68 small earthquakes. As these data were inadequate to compute empirical transfer functions using the standard spectral ratio (SSR) technique, we explored the possible use of horizontal-to-vertical spectral ratios (HVSR). First, we compare HVSR computed from theoretical transfer functions for incident P, SV, and Rayleigh waves with the horizontal transfer function for each incidence type. Second, we compute HVSR for our weak-motion data set and show that the results are stable, with a scatter not larger than that usually accepted in SSR studies. We observe significant differences between N-S and E-W motion. When we compare HVSR with theoretical transfer functions, we obtain a better agreement for SV motion than for SH motion. Amplification levels are similar between HVSR and predicted amplification, even for the SH case. This suggests that discrepancies that have been signaled for the topographic amplification between observations and predictions could be due to site effects being present in the reference station used to computed SSR. Our results support the use of HVSR to determine topographic site effects. Thus, HVSR may have a large potential to evaluate site effects in a wider variety of geological conditions than previously thought, without the shortcomings of SSR. Finally, we show that HVSR computed from noise recordings gives a reasonable estimate of HVSR computed from weak-motion data. Although this conclusion should be better substantiated, our preliminary results are encouraging.

Microtremor

Harmonic

10.1785/bssa0860051559

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Citations (126)

Shear-wave Velocity Structure around Teide Volcano: Results Using Microtremors with the SPAC Method and Implications for Interpretation of Geodetic Results

Birkhäuser Basel eBooks (2007)

Francisco J. Chávez‐García Francisco Luzón Dimitrios Raptakis José Fernández

Deformation analysis and simulation of volcanic edifices require the construction of models of elastic properties of those structures. In this paper we present an analysis of microtremor measurements recorded during the performance tests of two temporary seismic arrays installed in the eastern portion of the Teide caldera in 1994. We take advantage of recent developments of the SPAC method and use spatial cross-correlation computations to estimate phase velocity dispersion of Rayleigh waves at the location of the arrays. We show that the extension of the standard SPAC method is valid in the case of our data, justifying its use and supporting the generalization of the SPAC method to single station pairs. The phase velocity dispersion curve obtained was inverted to recover the shear-wave profile at the site of the arrays. Our results indicate that the subsoil structure of the caldera is laterally homogeneous at the scale of a few km about the location of the arrays. We obtained about 315 m of volcanic sediments overlying rocks with a shear-wave velocity of 2 km/s. These results are robust and are a starting point to further modelling of deformation, permanent or transient, at this volcanic edifice, which can be useful in the interpretation of different observed fields. In fact, the computation of deformations and gravity changes due to possible volcanic intrusions in two models; one considering the volcanic sediments and the other without considering them, provided different results in the near field.

Caldera

Rayleigh Wave

Microtremor

10.1007/978-3-7643-8417-3_5

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Citations (0)

Effect of soil conditions on predicted ground motion: Case study from Western Anatolia, Turkey

Physics of The Earth and Planetary Interiors (2014)

Elçin Gök Francisco J. Chávez‐García Orhan Polat

Strong ground motion

Seismic risk

10.1016/j.pepi.2014.01.011

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Citations (31)

On the correlation of seismic microtremors

Journal of Geophysical Research Atmospheres (2005)

Francisco J. Chávez‐García Francisco Luzón

We present results of the analysis of microtremor measurements using a small array. Our analysis is based on the computation of cross‐correlation functions between stations in both frequency and time domains. We obtain similar results in both domains and link those results to the application of Aki's spatial autocorrelation method of using a single station pair and to recent studies that have shown that the Green's function between two stations can be retrieved from the temporal cross correlation of seismic noise. We show that the same simple subsoil structure allows interpretation of our correlation results in time and frequency. We observe both Love and Rayleigh waves; however, Love waves dominate the records in our lower‐frequency range (between 3.6 and 6 Hz), while Rayleigh waves are prevalent in the records in our higher‐frequency band (from 6 to 20 Hz). Frequency domain cross correlation yields better results in the lower‐frequency range, while time domain cross correlation shows very clear results in the higher‐frequency band. Thus both analyses are complementary. Our results show that ambient vibration recorded at the free surface includes different types of waves but that the correlation between any two stations is governed by the more stable propagation mode between them, surface waves in the case of a layered medium. Our results shed some light on the nature of microtremors and on the reasons why the spatial autocorrelation method or the horizontal‐to‐vertical spectral ratios are useful in geophysical and site response studies.

Microtremor

Rayleigh Wave

Seismic Noise

Microseism

Cross-correlation

Frequency band

Love wave

10.1029/2005jb003671

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Citations (85)

Earthquake ground motion in Mexico City: An analysis of data recorded at Roma array

Soil Dynamics and Earthquake Engineering (2006)

Martín Cárdenas‐Soto Francisco J. Chávez‐García

Mexico city

Uncorrelated

Strong ground motion

10.1016/j.soildyn.2006.09.003

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Citations (4)

Topographic site effects. A comparison of two nonreference methods

Bulletin of the Seismological Society of America (1997)

Francisco J. Chávez‐García Miguel Rodríguez E. H. Field D. Hatzfeld

Abstract We present an experimental study of topographic site effects. The data we use come from an experiment carried out during the summer of 1989, in Epire (northern Greece). Ten digital stations recorded a total of 68 small earthquakes. A recent article (Chávez-García et al., 1996) presented a comparison between site effects determined using horizontal-to-vertical spectral ratios (HVSR) for this data set and theoretical modeling. In this note, we compare the topographic site effects determined using HVSR with another, independent, experimental estimate: a generalized inversion scheme (GIS). Neither HVSR nor GIS depend on the availability of a reference site. We obtain a very good agreement between both estimates of topographic site effects for both horizontal components. Our results support the use of HVSR to determine topographic site effects.

Microtremor

10.1785/bssa0870061667

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Citations (52)

Journal of Seismology (2000)

Francisco J. Chávez‐García Ezio Faccioli

Allowance (engineering)

Code (set theory)

Building code

Site selection

Eurocode

10.1023/a:1009830201929

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Citations (90)

Local amplification and subsoil structure at a difficult site: Understanding site effects from different measurements

Soil Dynamics and Earthquake Engineering (2016)

Francisco J. Chávez‐García Dimitrios Raptakis

Ambient noise level

Microtremor

Subsoil

Seismic microzonation

Seismic Noise

Amplification factor

10.1016/j.soildyn.2016.10.008

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Citations (7)

The Mexico Earthquake of September 19, 1985—A Theoretical Investigation of Large- and Small-scale Amplification Effects in the Mexico City Valley

Earthquake Spectra (1988)

Pierre‐Yves Bard Michel Campillo Francisco J. Chávez‐García Francisco J. Sánchez‐Sesma

The linear, large-scale and small-scale amplification effects in the Mexico City valley, related to both the surficial clay layer and the underlying thick sediments, are investigated with two-dimensional (2D) models and compared with the results of simple one-dimensional (1D) models. The deep sediments are shown to be responsible, on their own, for an amplification ranging between 3 and 7, a part of which is due to the 2D effects in case of low damping and velocity gradient. This result is consistent with the observed relative amplification around 0.5 Hz at CU stations with respect to TACY station. The amplification due to the clay layer is much larger (above 10), and the corresponding 2D effects have very peculiar characteristics. On the one hand, the local surface waves generated on any lateral heterogeneity exhibit a strong spatial decay, even in case of low damping (2%), and the motion at a given site is therefore affected only by lateral heterogeneities lying within a radius smaller than 1 km. On the other hand, these local 2D effects may be extremely large, either on the very edges of the lake-bed zone, or over localized thicker areas, where they induce a duration increase and an overamplification. The main engineering consequences of these results are twofold: i) microzoning studies in Mexico City should take into account the effects of deep sediments, and ii) as the surface motion in the lake-bed zone is extremely sensitive to local heterogeneities, 1D models are probably inappropriate in many parts of Mexico City.

Length scale

10.1193/1.1585493

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Citations (172)

Site Effects and Building Damage Characterization in Concepción after the M_w8.8 Maule Earthquake

Earthquake Spectra (2015)

Gonzalo Montalva Francisco J. Chávez‐García Andrés Tassara Darío M. Jara Weisser

The influence of site effects on seismic demand was studied in Concepción to explain the observed damages suffered by engineered structures during the 2010 M w 8.8 Maule, Chile, earthquake. Shallow shear-wave velocity ( V S ), site period, and gravity measurements were used to assess site effects. The three-dimensional (3-D) basin shape was inverted from gravity values. Predominant period shows a good correlation with bedrock depth, suggesting that V S of soil is relatively uniform throughout the city. This was confirmed by direct V S measurements at 17 sites throughout the city. The irregular distribution of damage suggests that V S30 is not a good proxy for damage distribution in Concepción. In contrast, we observe dependence with basin thickness, site period, and estimated PGV for buildings with high vulnerability. Most low-vulnerability structures showed no damage regardless of site conditions and intensity measures. Our results indicate that site effects contributed to structural damage in vulnerable structures and these effects were primarily controlled by basin depth.

Bedrock

10.1193/101514eqs158m

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Citations (26)