Wednesday was the 91st anniversary of an earthquake that devastated our region and caused hundreds of deaths. In the past month the Dead Sea Transform fault system, also known as the Dead Sea Rift, has come to life, releasing energy in a chain of dozens of tremors, at least six of which could be felt. These tremors may not have caused damage, but do they portend stronger activity in the near future? There’s no way to know for sure, but there are signs that predictions of a destructive quake within a few months are not unfounded.
A quake occurs when the earth’s crust is torn in the wake of constant movement of the strong, hot material in the mantle just below the crust. The seismic waves released from the ruptured area spread from the earth to the surface, shaking buildings and hearts.
Many devastating earthquakes were preceded by irregular seismic activity in the rupture area. A cluster of numerous smaller temblors focused within a small area is unusual, and could herald a major quake.
This can be compared to fibers splitting under tension in a seam about to tear. The Dead Sea Rift is seen as a seam between tectonic plates — those huge lumps of the globe’s external crusts: the Arabian and the African plates.
A group of Russian scientists has developed an experimental method to predict an earthquake by monitoring irregular activity. They calibrate the definition of a tremor chain in a given area according to the extent of success in predicting quakes retroactively. This ongoing research has shown that in most cases, before a devastating quake, a chain of tremors occurs, but not every chain definitely heralds a destructive quake. In quake-prone areas, like Japan and California, the system’s forecast ability is limited, due to the frequency of small tremors. But in regions such as ours, where the activity is moderate, the system displays a promising predictive potential.
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In 2004 the Russian scientists published an article about how they forecast an extremely devastating quake in Japan in 2003. They demonstrated, based on the records of the Geophysical Institute of Israel, how after a chain of tremors from February to June 1995 in the Gulf of Eilat, the strongest earthquake in the past century struck our region in November of that year.
The Hebrew University joined the experiment, and a research student found that a tremor chain had heralded a medium quake in 1993, in the southern Bay of Eilat. Those quakes fortunately stemmed from ruptures in the sea bed, and the damage to the population was limited.
What has been happening in our region over the past month can clearly be described as a tremor chain. If it heralds a destructive earthquake we’ll know only after the fact, if it occurs in the next few months. Still, such a chain is an opportunity for each of us to review our readiness and to prepare for the impending disaster. That, because the answer to the question “will there be a devastating earthquake here?” is unequivocally yes, even if we cannot say when it will happen.
The energy accumulated in the fault line between the plates is increasing with time, and the energy released by the small tremors does not lessen the danger. Even if it takes time, the earthquake will happen. I don’t know if it will be very soon, but the danger is clear and present.
Amotz Agnon is a professor of geology and geophysics at the Hebrew University of Jerusalem.