- © 2014 by the Seismological Society of America
Operational earthquake forecasting (OEF) is the practice of continual updating and dissemination of physics‐based short‐term (days) probabilities for the occurrence of damaging earthquakes. Although fully appreciating the noble intention of OEF and the scientific merits of the seismicity analyses it employs, we are concerned that its wide promotion may lead the public to believe that earthquake preparedness can fluctuate at timescales of days or weeks.
Scientists who support OEF do recognize the importance of long‐term (decades and centuries) forecast. Jordan (2013) points out that long‐term forecasting can “guide earthquake safety provisions of building codes, performance‐based seismic design, and other risk‐reducing engineering practices, such as retrofitting to correct design flaws in older buildings.” However, they also believe that “properly done, short‐term forecasting complements long‐term seismic‐hazard analysis in promoting earthquake preparedness” and that “the age of OEF has arrived” (Jordan, 2013). Although to some extent short‐term forecasting is a worthwhile research subject, we question the claim that it should and can be made operational.
A typical OEF warning would announce that the probability of an earthquake of certain magnitude happening in a given region over the next few days has increased from negligibly small values (such as 0.001%) to a larger value (such as 5%; Jordan and Jones, 2010). The probability gain of several orders of magnitude is thought to be useful for communicating risk to the public and enhancing preparedness. We have two concerns over this type of warning.
First, warnings of this type send and reinforce a wrong message, that is, if scientifically estimated probability is very low, such as 0.001%, the public can afford to be less prepared for damaging earthquakes. OEF is based largely on analyses of earthquake clustering, or potential foreshock sequences, but the majority of damaging earthquakes are not preceded by anomalous foreshocks. Tragic examples include the 1976 Tangshan and 2010 Haiti earthquakes, each responsible for some quarter million deaths, and the 2008 Wenchuan, China, earthquake that caused about 80,000 deaths (Chen and Wang, 2010). Because of the absence of recognizable foreshock sequences, OEF would have had difficulty forecasting anomalously high probabilities prior to these events.
Second, a change from practically impossible (0.001%) to very unlikely (5%) is not useful for saving lives. The most objective measure of the usefulness of a short‐term forecast is whether it can guide preseismic evacuation of unsafe buildings. As is well known, the indictment of six Italian seismologists was for their perceived role of impeding some L’Aquila residents’ decision to evacuate their vulnerable dwellings. However, we cannot encourage communities to evacuate while telling them that such a decision will almost certainly (95%) be wrong, although there is a tiny chance that it could be right, as in the case of the fortuitous success in predicting the 1975 Haicheng earthquake using foreshocks (Wang et al., 2006). Even if we could provide probability forecasts of 20% or 40%, a decision to evacuate would still be a gamble, which society and economy could hardly afford. If an evacuation order was issued, but the said earthquake did not happen after a few days or weeks, it would be equally difficult to make a decision to lift the order. Crying earthquake (wolf) is a potent way of blunting earthquake awareness and preparedness. It is also an effective way of disrupting economy, for which there have been too many bad examples, such as in the aftermath of the M 7.8 Tangshan, China, earthquake of 1976 (Chen and Wang, 2010). Analyzing various social‐economic factors and using the 2009 L’Aquila event as an example, van Stiphout et al. (2010) concluded that “evacuation as mitigation action is rarely cost‐effective.”
Let us assume, in a region of high risk identified by a national seismic‐hazard model, there is a building that we think is very likely to collapse if a damaging earthquake strikes. What mitigation strategy can be suggested to its residents? Strategy 1: Use at your own risk. If you feel threatened by an increase in small earthquakes, avoid using the building for a few days or months. This seemingly absurd option unfortunately sees practice in real life, such as in L’Aquila. Strategy 2: You should make time‐dependent decisions on whether to stay in that building in accordance with “authoritative, scientific, consistent, transparent, and timely” probability forecasts, and/or follow civil authorities’ directives based on these forecasts. As discussed above, this is neither wise nor practical. Strategy 3: You, the government, and society should make every effort to retrofit or replace this building to comply with earthquake resistance provisions.
Strategy 3 is obviously the most sensible, but following this strategy is not simple, because there are many scientific, regulatory, and financial challenges. We think the scientific community should help society to deal with these challenges, not to champion short‐term alternatives. There are excellent examples to show that strategy 3 can work to a high degree of success. During the 2010 M 8.8 Maule, Chile, and the 2011 M 9.0 Tohoku‐Oki, Japan, earthquakes, very few modern buildings collapsed in strong ground shaking because of the proper design and implementation of building codes. As a result, fatalities due to building collapse were relatively small given the size of the earthquakes. Devastation caused by tsunamis following both events, especially in the case of the Tohoku‐Oki earthquake, is a different issue, which we do not address in this article.
Except for warning against damaging aftershocks after large earthquakes (Reasenberg and Jones, 1994), we question the operational value of any short‐term earthquake forecasting, no matter whether it is in the form of specific predictions or probability values. Society has very limited capacity in dealing with uncertain short‐term earthquake forecasting because of severe consequences of any wrong decisions of mitigation action. This is fundamentally different from dealing with daily weather forecasts. Preparedness for bad weather can indeed fluctuate on a daily or even hourly basis, and society can tolerate bad weather forecasts to a considerable degree. Ideas of low‐impact short‐term mitigation, such as targeted evacuation of vulnerable buildings and discreetly mobilizing rescue teams, seem impractical. For matters of life and death, partial measures would trigger runaway reactions among the public, especially in the age of social media. The value of official forecasting in quelling earthquake rumors and amateur predictions is also questionable. It seems unrealistic to expect the public to ignore sensational forecasts on the basis of official forecasts, which are authoritatively promised to be very uncertain.
The damage and fatalities caused by the L’Aquila earthquake again prompted us to reflect on our effort of promoting strategy 3. Relevant questions to ask are: Why did those buildings collapse? What could have been done better in designing and implementing building codes? How should retrofitting regulations and practices be improved to reduce the vulnerability of old buildings? How can the methods of developing seismic‐hazard models be further improved? Understandably, traumatized local communities tend to overlook these long‐term questions but focus on what could have been done just prior to the earthquake to save lives, as most dramatically demonstrated by the prosecution of Italian seismologists. During this type of crisis, the scientific community should step up to guide public and government attention to the relevant questions asked above. It is our concern that their attention was guided farther away from these questions by the report of the International Commission on Earthquake Forecasting for Civil Protection (Jordan et al., 2011), which, in our view, incorrectly concludes that the L’Aquila incident demonstrated the need for OEF.
Short‐term earthquake forecasting and prediction thrive on people’s lack of confidence in the safety of their buildings (Fig. 1). As long as there are vulnerable buildings, there will always be perceived need for short‐term forecasting, no matter how persistently such forecasting fails to demonstrate its value. Conversely, as seismic‐hazard assessment, building codes, and hence construction quality improve with scientific research, the perceived need for short‐term forecasting will continue to diminish.
Society’s best strategy against the consequence of earthquakes is to focus on making the built environment earthquake resistant. Practical methods to minimize the consequences of ground shaking, such as sending early warning signals after the initiation of a rupture, can play important supporting roles. With regard to forecasting, our view can be summarized as follows. (1) In mitigating seismic risk, the goal is to let people stay in their buildings without fear and without getting hurt, not to tell people when to escape from their buildings. (2) Forecast of seismic hazard should be made over decades and centuries, so that society knows how to strengthen the built environment within economic constraints. (3) Except for aftershocks, the scientific community has no authoritative role to play in providing forecasts over days and weeks.
This is Geological Survey of Canada contribution 20130308.