The Mexico Earthquake of September 19, 1985—An Empirical Model to Predict Fourier Amplitude Spectra of Horizontal Ground Motion

Castro, Raúl R.; Singh, S. K.; Mena, E.

doi:10.1193/1.1585497

Cited by 24 publications

(13 citation statements)

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“…Several important issues, however, remained unresolved in the study of Singh et al (1988a). Because spectral ratios were studied, it was not possible to know which of the two earthquakes was anomalous in and near Mexico City, although the damage to the city and spectral regression of coastal earthquakes recorded in Ciudad Universitaria (CU), a hill-zone site in the city (Castro, Singh & Mena 1988), strongly suggested that the Michoacan earthquake was anomalous. Since the source displacement spectra were obtained by averaging the corrected spectra from stations at different azimuths and distances (Houston & Kanamori 1986a), any azimuthal variation of the anomalous ratio could not be resolved.…”

Section: Introductionmentioning

confidence: 99%

Evidence for anomalous body-wave radiation between 0.3 and 0.7 Hz from the 1985 September 19 Michoacan, Mexico earthquake

Singh

Mori

Mena³

et al. 1990

Geophysical Journal International

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S U M M A R YIn order to better understand the causes of unprecedented damage to Mexico City during the 1985 September 19 Michoacan earthquake (M, = 8.0) spectral ratios of teleseismic P-waves of this earthquake are studied with respect to those from five recent, large Mexican subduction zone earthquakes (7.0 5 M, I 7.7). The data are from vertical-component digital seismographs. It is found that the spectral ratios at stations in the NE quadrant are anomalously more energetic than those predicted by the o-* source model in the critical frequency range for Mexico City (0.3-0.7 Hz). The evidence is especially convincing for the spectral ratios with respect to the earthquakes of 1985 September 21 (M, = 7.6) and 1986 (M, = 7.0) since the data are available from several stations in the NE quadrant. The teleseismic P-wave spectral ratio in this quadrant with respect to the 1985 September 21 earthquake, in the critical frequency range, is close to the acceleration spectral ratio found in and near Mexico City (also in the NE quadrant). Velocity traces in the epicentral region of the Michoacan earthquake, obtained by integrating the accelerograms, also show oscillations with a frequency of about 0.4Hz. Furthermore, a regression study of Fourier acceleration spectra at a hill-zone site in Mexico City demonstrates that the Michoacan earthquake was anomalously energetic in the city at the critical frequencies for an event of that magnitude and at that distance. If the data from 7.0 I M, 5 7.7 events can be extrapolated to estimate the ground motions from M, L 8.0 earthquakes, then the evidence, supports an anomalously large body-wave radiation towards Mexico City between 0.3 and 0.7 Hz during the Michoacan earthquake. This anomalous radiation and the dramatic local amplification of seismic waves in the lake-bed zone of the city (-10-50 times at frequencies between 0.3 and 0.7Hz) appear to be the principal natural causes of the disaster. The anomalous teleseismic P-wave spectral ratios with respect to the earthquakes of 1985 September 21 and 1986 found in the NE quadrant are not observed in the data available from a small number of stations in the other quadrants. If this observation is true then it suggests a directional property to the anomalous radiation.

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Section: Introductionmentioning

confidence: 99%

Evidence for anomalous body-wave radiation between 0.3 and 0.7 Hz from the 1985 September 19 Michoacan, Mexico earthquake

Singh

Mori

Mena³

et al. 1990

Geophysical Journal International

Self Cite

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“…The earthquake was the second largest in Mexico during the 20th century (Singh et al 1988a). The amount of released energy was anomalously high (Singh et al ibid;Singh et al 1987;Castro et al 1988). The energy rose to twice its average value at frequencies near 0.5 Hz.…”

Section: The 1985 Earthquakementioning

confidence: 94%

Seismic response of the Mexico City Basin: A review of twenty years of research

Estrella

Yussim²,

Lomnitz

2006

Nat Hazards

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Mexico City, political and economic center of Mexico, was founded in a lake, at more than 2000 m above sea level. The lacustrine mud under the downtown area is associated with high seismic risk. Twenty years after the destructive 1985 earthquake (Ms = 8.1) we review published research on seismic response in the Mexico Basin, especially seismic and microtremor studies on soft ground and the influence of the seismic response of lake mud on damage.

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“…The first attenuation law to estimate Fourier amplitude spectra at station CU, in the hill zone of Mexico City, was due to Castro et al [1988]. Ordaz et al [1994] improved the prediction using more data and a Bayesian regression approach: with the predicted Fourier amplitude spectra, the use of random vibration theory and an estimation of the duration of motion, it is possible to compute response spectra (Method 2).…”

Section: Computation Of Elastic Response Spectra At Hill Zone (Cu)mentioning

confidence: 99%

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JAIMES¹

2006

J. Earth. Eng.

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We compare four methods, all based on Bayesian regressions, to predict response spectra at instrumented sites, located at the hill and lakebed zones in Mexico City, that have recorded several recent earthquakes. The regressions are built as functions of magnitude and closest distance to the rupture area of the earthquake, using more than 20 subduction earthquakes (thrust-faulting mechanism) recorded since 1964. The four methods are: (1) a regression on observed response spectra; (2) a regression on observed Fourier amplitude spectra and use of random vibration theory to estimate the response spectra, (3) a regression on observed response spectra at the reference hill-zone station multiplied by response spectral ratios; and (4) a regression on Fourier amplitude spectra at the reference hill zone, multiplied by Fourier spectral ratios and use of the random vibration theory to estimate response spectra.

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The Mexico Earthquake of September 19, 1985—An Empirical Model to Predict Fourier Amplitude Spectra of Horizontal Ground Motion

Cited by 24 publications

References 0 publications

Evidence for anomalous body-wave radiation between 0.3 and 0.7 Hz from the 1985 September 19 Michoacan, Mexico earthquake

Evidence for anomalous body-wave radiation between 0.3 and 0.7 Hz from the 1985 September 19 Michoacan, Mexico earthquake

Seismic response of the Mexico City Basin: A review of twenty years of research

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