A quake measuring 4.5 on the Richter scale shook northern Israel on Monday morning, well short of fatal levels but still noticeable to people in the area. It was the strongest of the minor earthquakes that have been shaking the area around the Sea of Galilee for several days.
Earthquake strength is described in logarithmic Richter scale terms, and is a function of the energy the quake releases. A quake measuring a magnitude of 5 is 10 times more powerful than a quake measuring 4, and is 100 times more powerful than a quake measuring 3.
Usually earthquakes rated less than 6 on the Richter scale cause little to no damage or casualties, though much depends on the local infrastructure and soil type.
Israel sits right on the Dead Sea fault. The Dead Sea itself and the Sea of Galilee, a freshwater lake, both lie right along that fault, which stretches from Africa to Turkey.
The Dead Sea fault has generated deadly quakes in the past, the most recent in 1927, which measured 6.3 on the Richter scale. Hundreds of people were killed. A temblor in 1837 leveled the cities of Tiberias and Safed.
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A big earthquake is going to hit Israel and Jordan at some point. The question is when, but nobody can even hypothesize about that at this stage. Theoretically, the Dead Sea fault generates a significant temblor every 80 to 100 years, geologists say. In other words, from the perspective of statistics, it is overdue.
The swarms of quakes began in Israel last Wednesday morning, when 11 tremors were recorded, the strongest being 4.1 on the Richter scale.
But swarms, some originating 10 kilometers beneath the Earth's surface, do not necessarily portend that the "big one" is imminent. Swarms usually subside, as happened in 2013, says Yariv Hamiel, head of Geological Hazards at the Israel Geological Institute. Swarms are not considered predictive of a big quake to come; rarely, a swarm of small tremors may be followed by a major temblor.
Affecting land and the living
A major earthquake can affect the land and the living in several ways. It may cause the surface of the Earth to crack along the active fault, which is one scenario threatening the Red Sea resort city, Eilat. It too sits on the Dead Sea fault.
An additional potential danger is a landslide, which could, in Israel's case, threaten Tiberias and Safed. Yet another problem is amplification, a scenario predicted for the Jezreel Valley in the northern part of the country.
Then there is liquefaction, when the soil behaves like liquid. This can happen during an earthquake, for instance, in cities built on landfill or water-heavy soil. This sort of phenomenon threatens the Bay of Haifa, for instance, and parts of the Israeli coast.
A final danger of quake is a tsunami, which isn't likely to ensue from a temblor along the Dead Sea fault, but is a general danger that every coastal country faces. It bears noting that a large lake can produce tsunamis, too, if a landslide spills into one, for instance.
In contrast to erroneous conventional wisdom, tsunamis do happen in the Mediterranean Sea. Debris found above Phoenician graves in Tel Achziv, northern Israel, suggest that a tsunami hit the Israeli coast 2,800 years ago.
Earthquakes are a lot more frequent than tsunamis: In fact, Israel experiences them just about every day, but most are too small to be noticed by anything but sensors. Quakes still cannot be predicted at all, though work is being done around the world with that aspiration in mind.
However, in the case of powerful temblors, lives can be saved if people take shelter after being warned the second the quake begins. Israel is in the process of installing an earthquake-alarm system called Tru'a, which will be fed information from 120 seismic sensors placed along the Dead Sea Valley and up to the Sea of Galilee, in the Jordan Valley and on Mount Carmel.
When a quake begins and is detected by the system, alerts will be sent to the Home Front Command and disseminated among the general public, so people can take shelter. Jerusalem residents are expected to get about 10 seconds' advance notice, while in Tel Aviv – which is farther from anticipated epicenters – it could take as long as 25 seconds.