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5.5: Forecasting Earthquakes

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It has long been a dream of seismologists, geologists and public safety officials to be able to accurately predict earthquakes on time scales (weeks, days or hours) that would be useful for minimizing danger to the public and damage to infrastructure. Many different avenues have been explored, such as warning foreshocks, changes in magnetic fields, seismic tremor, changing groundwater levels, strange animal behavior, observed earthquake periodicity, stress transfer considerations and a range of others. So far, none of the research into earthquake prediction has provided a reliable method. Although there are reports of successful earthquake predictions, they are rare, and many are surrounded by doubtful circumstances.

The problem with earthquake predictions, as with any other type of prediction, is that they must be accurate most of the time, not just some of the time. We have come to rely on weather predictions because they are generally (and increasingly) accurate. But if we try to predict earthquakes and are only accurate 10% of the time (and even that isn’t likely with the current state of knowledge), the public will lose faith in the process very quickly, and then all the predictions will be ignored.

There was a great hope for earthquake predictions late in the 1980s, when attention was focused on part of the San Andreas fault at Parkfield, about 200 km south of San Francisco. Between 1881 and 1966 there were 5 earthquakes at Parkfield, most spaced at approximately 20-year intervals, all confined to the same 20 km-long segment of the fault and all very close to M6 (Figure 5.5.1). Both the 1934 and 1966 earthquakes were preceded by small foreshocks exactly 17 minutes before the main quake.

parkfield-1024x439.png
Figure 5.5.1: Earthquakes on the Parkfield Segment of the San Andreas Fault, 1881 to 2004.

The U.S. Geological Survey recognized this as an excellent opportunity to understand earthquakes and earthquake prediction, so they armed the Parkfield area with a huge array of geophysical instruments and waited for the next quake, which was expected to happen around 1987. Nothing happened! The “1987 Parkfield earthquake” finally struck in September 2004, about 17 years late. Fortunately, all the equipment was still there, but it was to no avail from the perspective of earthquake prediction. There were no significant precursors to the 2004 Parkfield earthquake in any of the parameters measured, including: seismicity, harmonic tremor, strain (rock deformation), magnetic field, the conductivity of the rock or creep, and there was no foreshock. In other words, even though every available technique was used to monitor it, the 2004 Parkfield earthquake came as a complete surprise, with no warning whatsoever.

The hope for earthquake prediction is not dead, but it was hit hard by the Parkfield experiment. The current focus in earthquake-prone regions is to provide forecasts of earthquake probabilities within a certain time period—typically a number of decades—and also to ensure that the population is educated about earthquake risks and that buildings and other infrastructure are as safe as can be. An example of this approach for the San Francisco Bay region of California is shown on Figure 5.5.2. Based on a wide range of information, including past earthquake history, accumulated stress from plate movement, and known stress transfer, seismologists and geologists have predicted the likelihood of a M6.7 or greater earthquake on each of 8 major faults that cut through the region. The greatest probabilities are on the San Andreas, Rogers Creek and Hayward faults. As shown on the diagram, there is a 72% chance that a major and damaging earthquake will take place somewhere in the region prior to 2043.

bay-area-prob.png
Figure 5.5.2: Probabilities of a M6.7 or Larger Earthquake on Various Faults in the San Francisco Bay Region of California, 2014 to 2043.

Japan established a nation-wide earthquake warning system in 2008, and the US Geological Survey started work on the ShakeAlert system for Washington, Oregon and California in 2016, and the systems are functional. Both systems are based on seismometers on land quickly picking up earthquakes near epicenters and warning nearby areas of the impending waves.

Media Attributions


  1. Province of British Columbia. Seismic Mitigation Program (last updated May 11, 2021). https://www2.gov.bc.ca/gov/content/e...ation#progress

This page titled 5.5: Forecasting Earthquakes is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Steven Earle (BCCampus) .

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