New constraints on the 1922 Atacama, Chile, earthquake from Historical seismograms

Creators: Kanamori, Hiroo; Rivera, Luis; Ye, Lingling; Lay, Thorne; Murotani, Satoko; Tsumura, Kenshiro

Abstract

We recently found the original Omori seismograms recorded at Hongo, Tokyo, of the 1922 Atacama, Chile, earthquake (M_S = 8.3) in the historical seismogram archive of the Earthquake Research Institute (ERI) of the University of Tokyo. These recordings enable a quantitative investigation of long-period seismic radiation from the 1922 earthquake. We document and provide interpretation of these seismograms together with a few other seismograms from Mizusawa, Japan, Uppsala, Sweden, Strasbourg, France, Zi-ka-wei, China and De Bilt, Netherlands. The 1922 event is of significant historical interest concerning the cause of tsunami, discovery of G wave, and study of various seismic phase and first-motion data. Also, because of its spatial proximity to the 1943, 1995 and 2015 great earthquakes in Chile, the 1922 event provides useful information on similarity and variability of great earthquakes on a subduction-zone boundary. The 1922 source region, having previously ruptured in 1796 and 1819, is considered to have significant seismic hazard. The focus of this paper is to document the 1922 seismograms so that they can be used for further seismological studies on global subduction zones. Since the instrument constants of the Omori seismographs were only incompletely documented, we estimate them using the waveforms of the observed records, a calibration pulse recorded on the seismogram and the waveforms of better calibrated Uppsala Wiechert seismograms. Comparison of the Hongo Omori seismograms with those of the 1995 Antofagasta, Chile, earthquake (M_w = 8.0) and the 2015 Illapel, Chile, earthquake (M_w = 8.3) suggests that the 1922 event is similar to the 1995 and 2015 events in mechanism (i.e. on the plate boundary megathrust) and rupture characteristics (i.e. not a tsunami earthquake) with M_w = 8.6 ± 0.25. However, the initial fine scale rupture process varies significantly from event to event. The G1 and G2, and R1 and R2 of the 1922 event are comparable in amplitude, suggesting a bilateral rupture, which is uncommon for large megathrust earthquakes.

Additional Information

© 2019 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2019 July 2. Received 2019 June 28; in original form 2019 February 20. Published: 03 July 2019. The Omori seismograms used in this study were made available to us by the historical seismogram archive at the Earthquake Research Institute, the University of Tokyo. We thank Kenji Satake and the staff of the archive. We thank Toru Matsuzawa and Tomotsugu Demachi at Tohoku University for making available to us the Mizusawa Omori seismograms, and Bernard Dost at the Royal Netherlands Meteorological Institute, Susan Beck at the University of Arizona and Björn Lund at Uppsala University for helping us study De Bilt seismograms and Uppsala seismograms (1922 and 2015). We thank Javier Ruiz at the Universidad de Chile for helping us locate Sieberg & Gutenberg (1924), and Nobuo Hamada for prividing us with a copy of the Observatory Manual of the Central Meteorological Agency, Japan, published in 1936. The copies of the Gutenberg notepad used in this study are provided by the Archives of the California Institute of Technology. The Data Management System of the Incorporated Research Institutions for Seismology (http://www.iris.edu/hq/) was used to access the seismic data from the Global Seismic Network and Federation of Digital Seismic Network stations. The F-net data used in this study were provided by the National Research Institute for Earth Science and Disaster Prevention (NIED) of Japan. T. Lay's research on earthquakes is supported by U.S. National Science Foundation grant EAR1802364. L. Ye's research on earthquakes is supported by National Science Funding of China (NSFC) grant No. 41874056. We thank the editor, Dr. Huajian Yao, and two anonymous reviewers for encouraging comments on our manuscript.

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