The great Mexican earthquake of 19 June 1858: Expected ground motions and damage in Mexico City from a similar future event

Abstract

The description of the great earthquake of 19 June 1858 is unusual: damage and high intensities were reported both in the state of Michoacan and in Mexico City. Although a coastal epicenter for this earthquake cannot be ruled out, the reports agree better with an intermediate-depth (about 50 km), normal-faulting event in the subducted Cocos plate. A careful examination of the reports of this event and other normal-faulting events below the Mexican altiplano suggests that a likely location is 18.0 °N, 100.8 °W, near the epicenter of the 6 June 1964 (M7.3, H = 55 km) event. This location is 220 km SW of the city. The magnitude of the earthquake is estimated to be about 7.7. We synthesize expected ground motions in CU, a hill-zone site in the city, from an event similar to that of 1858, using records from the 23 May 1994 earthquake (18.0 °N, 100.6 °W, H = 50 km, M5.7) as an empirical Green's function and stress parameter, Δσ, of 50, 160, and 300 bar. The expected peak horizontal acceleration in CU of Δσ = 160 bar is about 30 gals. Similar acceleration was recorded in CU during the 1985, Michoacan earthquake (M8.0). We compute expected ground motions at many sites in Mexico City using empirical transfer functions and random vibration theory and compare these motions and the expected damage in the city with those from the 1985 Michoacan earthquake. Results show that the overall expected damage during the postulated earthquake is ⅔ and 1⅓ of that during the Michoacan earthquake for Δσ = 160 and 300 bar, respectively. A greater percentage of low-rise construction, which constitute about 80% of the total in the city, will be damaged during the postulated earthquake than during the Michoacan earthquake. The expected ground motions for Δσ = 50 bar are smaller at all periods than those from the Michoacan earthquake. As the present building code for Mexico City contemplates coastal earthquakes of magnitude greater than 8.0, the case of Δσ = 50 bar is not of interest in this article. This preliminary study suggests a need for a more careful evaluation of expected ground motion in the Valley of Mexico from the postulated earthquake and its impact on the current design spectra of the city.

Definición del campo de esfuerzos-deformación y sismotectónica del sistema de fallas Morelia-Acambay, México

“…Hasta la fecha sólo algunas fallas han sido reconocidas como activas durante el Cuaternario tardío, y sólo algunas han sido asociadas a eventos sísmicos históricos (Dobson y Mahood, 1985;Sánchez-Garcilazo, 2000;Garduño-Monroy et al, 2009;Singh et al, 1996;Suter et al1992, Suter, 2001. Sin embargo, en este sector se han presentado varios sismos ligados a rupturas superficiales que se asocian a la tectónica transtensional de la FVTM (Ego y Ansan, 2002;Rodríguez-Pascua et al, 2010), sobre todo como producto de la actividad del sistema de fallas Morelia-Acambay.…”

Morfología Urbana, Daños en Estructuras, Sismicidad Y Red Acelerométrica De La Ciudad De Morelia

“…Se encuentra ubicada en una de las regiones de mayor sismicidad de la República Mexicana. Garduño y Escamilla (1996) mencionan que en el periodo de 1786 a 1899 se registraron 34 movimientos sísmicos, de éstos, se consideraron como de fuerte intensidad los registrados en 1786, 1858, 1873, 1875, 1887, 1894 y 1896. El temblor del 19 de junio de 1858, considerado inicialmente con origen de intraplaca (Singh, Ordaz y Pérez-Rocha, 1996), y posteriormente de origen cortical dentro de la Faja Volcánica Transmexicana, con epicentro considerablemente más cercano a Morelia (Suárez, Caballero y Novelo, 2019), provocó daños importantes asociados a una intensidad estimada de IX en la escala de Mercalli (Jara y Jara, 2007). Las crónicas (Contreras, 1989) que describen los daños que produjo este sismo enfatizan que "donde se hizo sentir más fue en Pátzcuaro, donde el sacudimiento causó terribles efectos, arruinando varios templos y casas.…”