Reply to ‘Comment on “Evidence for a large strike-slip component during the 1960 Chilean earthquake” by H. Kanamori, L. Rivera and S. Lambotte’ by J. C. Savage

Abstract

We thank Dr Jim Savage for his interest in, and comment on, our paper (Kanamori et al. 2019, hereafter referred to as KRL19), where we showed that the commonly believed thrust-fault mechanism of the 1960 Chilean earthquake (Mw = 9.5) is not compatible with teleseismic data (e.g. strain seismograms at Isabella, California, and Ogdensburg, New Jersey, and long-period seismograms at Pasadena, California and Berkely, California) and suggested that dextral-slip component comparable in amount to the dip-slip component is required. We did not test our model against the shear strain data in Chile published in Plafker & Savage (1970). Savage (2021, hereafter referred to as S21) investigated whether the large dextral slip is compatible with the observed shear strain data. He concluded that the observed shear strain was very small, and provides no obvious evidence for large dextral component. However, he also stated that the absence of shear strain is not conclusive evidence of the absence of dextral slip. In fact, using a 2-D model, he showed in his fig. 9 that models with strike-slip moment comparable to the thrust moment can fit the observed uplift and strain data well. However, he noted that these models require remarkable balancing of contributions from the shallower (depths <∼70 km) and deeper strike-slip components. Savage thinks that such near-perfect cancelling is unlikely. Also, the distribution of the dextral slip shown in fig. 9 may appear somewhat unrealistic because it is very different from that of dip slip.