Re‐examination of the 1928 Parral, Mexico earthquake (M6.3) using a new multiplatform graphical vectorization and correction software for legacy seismic data

The seismic gap hypothesis has been widely cited in Mexico to predict the location of future earthquakes. However, no analysis of the outcome of any predictions of the hypothesis in Mexico has been done to date. This work analyzes the outcome of the prediction by Nishenko and Singh (1987a), which is based on probability distribution functions over time in defined segments that allow for a formal evaluation. Specific probabilities were given for 5, 10, and 20 yr after 1986, using the cumulative distribution function. The prediction relies on the precise repeat times of characteristic earthquakes to define the segments, but we show that the catalog the authors use relies on an imprecise definition of characteristic earthquakes. We discuss some of their decisions in building their catalog to explain how we analyze the outcome of the prediction. An unexpected result is that the very catalog the authors use to create the gap hypothesis prediction does not seem to support a narrow recurrence interval and instead seems to suggest large variability in earthquake recurrence intervals along the Mexican subduction zone. We generate null model earthquake catalogs using the average number of earthquakes that occur in the subduction zone and randomly distribute these along the segments according to their relative lengths. We find that the null model performs better than the seismic gap hypothesis prediction. No earthquakes occur in segments with a 70% or higher probability according to NS1987 (there were four such segments in the 20-year time frame), but an Mw 8.0 earthquake occurs in a segment with a less than 16% probability of an earthquake. We conclude that the gap hypothesis performed poorly at predicting earthquakes in Mexico and, in fact, its predictions were worse than predicting earthquakes by chance.

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A Source Study of the Mw 7.0 Acapulco, Mexico, Earthquake of 8 September 2021

Iglesias

Singh

Castro-Artola

et al. 2022

Seismological Research Letters

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The Acapulco earthquake of 2021 broke a segment of the southeast Guerrero seismic gap along the Mexican subduction thrust. The rupture initiated offshore Acapulco (16.770° N, 99.942° W) and propagated down-dip toward northeast. This source directivity is confirmed from both (1) an analysis of local and regional recordings as a function of azimuth and (2) kinematic inversion of near-source, band-pass filtered (0.025–0.5 Hz) displacement seismograms and Global Positioning System static coseismic displacement vectors. The inversion reveals little slip near the hypocenter (<0.5 m) and significant slip distributed over an area of ∼184 km2, with the large slip patches in the northeast part of the fault. The estimated average slip and static stress drop are 260 cm and 18.6 MPa, respectively. Moment rate function reported by National Earthquake Information Center–U.S. Geological Survey from finite-fault modeling is simple, and it resembles other Mexican subduction earthquakes in the 7.0 ≤ M ≤ 7.5 range. Moment rate spectrum is well fit by the Brune ω−2 source model. Radiated seismic energy from teleseismic P waves is 7.5×1014 J, and ER/M0 is 2.1×10−5. Radiated energy enhancement factor—a measure of source complexity—is small, 5.8, similar to other Mexican subduction thrust earthquakes. Seismograms at DeBilt of the 2021 and the 11 May 1962 Acapulco earthquakes show an extraordinary similarity, seldom seen at M 7.0 level. The 2021 earthquake seems a repeat of the 1962 earthquake. The slip deficit since 1962 corresponding to a plate convergence rate of 6.2 cm/yr and perfect coupling is 366 cm. Thus, the seismic slip of 260 cm during that 2021 earthquake suggests a coupling ratio of 0.7, greater than 0.3 and 0.5 reported from geodetic measurements. Large moment release in the southeast seismic gap appears to have a periodicity of ~60 yr. Because 60 yr have elapsed since the last sequence earthquakes (1957 MS 7.5; 1962 MS 7.0 and 6.8), a renewal of large earthquakes in the region may be expected.

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Re‐examination of the 1928 Parral, Mexico earthquake (M6.3) using a new multiplatform graphical vectorization and correction software for legacy seismic data

Cited by 6 publications

References 27 publications

The Arquive of Tatuoca Magnetic Observatory Brazil: from paper to intelligent bytes

The Arquive of Tatuoca Magnetic Observatory Brazil: from paper to intelligent bytes

A Test of the Earthquake Gap Hypothesis in Mexico: The Case of the Guerrero Gap

A Source Study of the Mw 7.0 Acapulco, Mexico, Earthquake of 8 September 2021

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