Macroseismic study of shallow earthquakes in the central and eastern parts of the trans-Mexican volcanic belt, Mexico

Abstract

We present isoseismal maps for eight shallow earthquakes (1887 Pinal de Amoles, 1912 Acambay, 1920 Jalapa, 1950 Ixmiquilpan, 1976 Cardonal, 1979 Maravatío, 1987 Actopan, and 1989 Landa; 4.1 ≦ mb ≦ 6.9) that occurred in the central and eastern parts of the trans-Mexican volcanic belt. Based on their intensity distributions, we can relate several of these earthquakes to east-west striking Quaternary normal faults known from geological observations. Furthermore, we derive for these events, by empirical curve fitting, linear relations between the magnitude calculated from the instrumental record, the intensity distribution, and the maximum intensity. The comparison of these relations with equations from the literature suggests that the area shaken with a certain intensity by an earthquake in the trans-Mexican volcanic belt is approximately 10 times smaller than the area shaken by a shallow earthquake of the same magnitude in the intracratonic part of North America. Moreover, we use the derived relationships between magnitude, isoseismal area, and maximum intensity to estimate the intensity magnitude Mi of the 1887 Pinal de Amoles earthquake as 5.3 ± 0.5.