Earthquake Immunity or False Sense of Security: A Historical California Retrospective
Abstract
A common theme in early 20th century conversations about earthquakes was that the occurrence of a large earthquake effectively immunized a region from future large events for decades if not generations. Especially during the period between 1906 and 1933 - i.e., after the San Francisco earthquake but before the Long Beach earthquake - this argument was made often by city boosters who wanted to allay fears about earthquake hazard after a damaging earthquake had occurred. But the argument was also sometimes made by scientists, for whom the conclusion appeared to be a logical consequence of Reid's elastic rebound theory. The formal seismic gap hypothesis (Sykes, 1971), introduced much later, continues to be the subject of heated debate. I consider the question, if Californians had banked on immunity following a locally damaging earthquake, how often would this reassurance have been borne out since the late 19th century, and how often would it have proved to be a false sense of security over the following 10 years? Over the following 30 years? To address this question I consider the catalog earthquakes above magnitude 6 in California since 1900, events for which magnitudes are constrained by at least some instrumental data as well as more abundant macroseismic observations. (From roughly 1900 onward, earthquakes as large as magnitude 5 were recorded by early instruments at Berkeley, so the state-wide catalog is assumed to be complete at the M6 level from 1900 onward.) In the future, it will be possible to address the question in more detail using historically observed intensity data, now being compiled by the California Historical Intensity Mapping Project (CHIMP; Salditch et al., 2018).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMNH43A..08H
- Keywords:
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- 4313 Extreme events;
- NATURAL HAZARDS;
- 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDS;
- 7212 Earthquake ground motions and engineering seismology;
- SEISMOLOGY;
- 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGY