Global Positioning System (GPS) measurements suggest hours-long precursors to many large earthquakes
BY QUENTIN BLETERY, JEAN-MATHIEU NOCQUET
Tsunami waves hit the coast in Fukushima Prefecture, Japan, after a powerful earthquake under the North Pacific Ocean.
PHOTO: ADATSUGU TOMIZAWA/JIJI PRESS/AFP/GETTY IMAGES
A meaningful earthquake prediction must clearly define the expected time, location, and magnitude of a future event (
1). Short-term earthquake prediction—that is, the capability to issue a warning from minutes to a few months before a mainshock—is impossible without the existence of an observable and actionable precursor. Thus, a key goal is the discovery of a common preparatory faulting process that can tell us where, when, and how big an impending earthquake is going to be (
2). On page 297 of this issue, Bletery and Nocquet (
3) present a systematic analysis of changes in horizontal position of approximately 3000 geodetic stations, which were measured by using the Global Positioning System (GPS), near 90 global earthquakes with magnitudes greater than 7. They found that on average, horizontal movements of the stations exponentially accelerated in a direction consistent with slow fault slip near the eventual earthquake nucleation point in the last 2 hours before the earthquake ruptures.
There is a long history of retrospective studies, carried out after a large earthquake has already happened, that suggests a wide variety of possible precursors that could potentially have been used to predict the earthquake (
2). In the 1970s, there was some optimism that observations of reliable precursors should be possible with improved geophysical observations, but that optimism waned in subsequent decades. There is a single case of an officially issued prospective prediction of a large earthquake, based largely on the observation of hundreds of small earthquakes, in the days preceding the 1975 Haicheng earthquake in China. Even then, luck apparently played a big role in the identification of these events as foreshocks (
4). Nonetheless, many earthquakes are preceded by foreshock sequences (
5), and a few of the largest earthquakes of the 21st century, including the 2011 magnitude 9 Tohoku-oki earthquake near the Japan Trench, followed slow faultslip episodes of varying sizes and durations (
6). That is, the fault that eventually ruptured and produced earthquake shaking sometimes started moving much more slowly before the mainshock.
In laboratory experiments (
7) and in computer models of earthquake ruptures (
8), such precursory activity is common. Recently, machine-learning methods were used to study acoustic signals emitted by laboratory faults and successfully predicted the time remaining before the next laboratory quake (
9). However, natural foreshocks cannot be distinguished from similar clusters of background seismicity (
10), and observed slow preslip events have not appeared different from geodetically measured slow slip transients that occurred without being followed by a large earthquake (
11). Overall, earthquake precursors in nature appear to be quite common, but they apparently come in a variety of flavors (
6) and have failed to reveal prognostic information that could be used to produce a short-term earthquake prediction (
12).
Sources from: SCIENCE.ORG
SVE NEWS is the leader in world news liberal sharing.
(Comments on this news are welcome)
2022 CWMALLS: Standard, Sharing,Ecology, Value;
2022 CWMALLS COMMODITY: Patent, Technology, Art, Intelligence;
2022 CWMALLS NEW SPECIES: Keen, Aggressive, Personality, Value;
2022 MWE FUND: Charity, Public Welfare, Responsibility
2022 CWS is with the world and Mars!
Tips: In order to explore more planet species diversity and ecosystem of Mars and earth’s biosphere of cohesion, from now on in the chosen experts and scholars of Mars and planets, especially the astrophysicist, astrobiologists, astrochemists, and so on all over the world’s elite, contribute to the existence and development of simulation of Mars landing. Thank you very much! CWS (Mars) Asia-Pacific Preparatory Committee 0086-57189877088/89877099, E-mail: mars@cws-mars.com, Twitter: CWS, October 3, 2021