Monday, February 21, 2011

Dead Sea Earthquakes – History, Archaeology and a Doomsday Prediction

A series of small earthquakes in the immediate Dead Sea area in the last two weeks of November, ranging between 3.0 and, allegedly, 5.1 (on November 20th 2007, which has more widely been reported as reaching a modest 4.5) on the Richter scale, has set off renewed worry about a major shake-up in the near future, and just how prepared we are for it.

The opinion camps can be divided quite smoothly into those predicting a significant earthquake within the next two decades or so, based hugely on Bible citations and an arbitrary pattern extracted from historical earthquakes along the Israeli side of the Dead Sea Transform, and those insisting – or maybe reassuring the public – that such minor tremors are far from indicators of a major quake, and that they are mainly functioning as regulatory measures to equalise the tension in this fault-rich area.

I know embarrassingly little about the mechanisms behind earthquakes,at least beyond basic plate tectonics taught in geography classes in secondary school; however, just a little research shows that it takes more than to select a small number of major quakes within the national boundaries of Israel to suggest a pattern and make doomsday predictions.

The list of earthquakes along the Jordan Valley is long – after all, the Dead Sea Rift isn’t a small one. Varve-counting and radiocarbon-dating of lacustrine sediments at the shore of the Dead Sea has found geological confirmation of most major historical and recent quakes above 6.0 on the Richter scale, and has found proxy data for quakes going as far back as the early 7th millennium BC (Migowski et al. 2004).

According to this, there has been a major tremor along the the Dead Sea Transform (DST) [from the Red Sea in the south to catching up with the East Anatolian Fault line in south-eastern Turkey] on average every one hundred years; this pattern is clearest for the last 2000 years or so, for when there is ample historical evidence for these natural disasters.

These have been spaced variably very close to the Dead Sea, but also up to about 400km along the rift, making for an even distribution of quakes across the Levant and thereby limiting the amount of damage done to the area. The intensity of the destructive capability equally depends on the depth of origin of the quake, and this is visible in the thickness of the disturbed sequences of sediment in the cores taken for analysis (Migowski et al. 2004: 308).

This research has allowed the extraction of a couple of interesting patterns of earthquake occurrences, which can be compared to the “historical basis” of the doomsday predictions of Israeli geologists.

Chronological Pattern.

Overall, the recurrence data from the Dead Sea suggest that the rate of seismic activity along the DST changed several times during the last 10,000 years. [Migowski et al. 2004: 311]

This is a very rough chronological outline.

1. Early Holocene (c. 8,000 – 5,500 BC): seismically quiet, although a bias in the accuracy of the core’s bottom levels might influence this picture. This was the time of the development and “perfection” of agriculture and animal domestication during the Aceramic and Ceramic Neolithic of the Levant. The suggestion has been made that the aggregation of people in so-called mega-sites in the later PPNB in Jordan (middle to late 7th millennium BC) was the result of an increased level of destruction in the Valley forcing migration up onto higher grounds (Rollefson pers. comm.); but no evidence for such settlements in the Jordan Valley have been found to confirm the earthquake hypothesis.
2. Later Prehistory (c.5,000 – 1 BC): moderately active, with a cluster of seismic activity between 1,000 and 2,100 BC. The Chalcolithic period (c. 4,500 – 3,600 BC), during which pastoralism flourished and a number of current staples became domesticated (e.g. olive), ended with a notable “collapse” of the settlement system then predominant, and transformed into the proto-urban Early Bronze Age (Levy 1995). An earthquake of some magnitude is mentioned around 4,000 BC in the upper Jordan Valley, although it’s relation to the transition/collapse needs to be further examined. The more active part of this later prehistoric period falls into the end of the Early Bronze Age (c. 2,000 – 1,600 BC), which is characterised by large-scale destruction and abandonment of the fortified towns of the time in favour of nomadic, small-scale settlement. The ruins at Pella (modern Tabaqat Fahl in the northern Jordan Valley) bear evidence of such destruction in the massive walls of the Bronze Age structures. While the map produced by Midowski et al. 2004 (see below) does not identify any significant quakes in the immediate vicinity of the site, the geological sequence indicates a serious of major shake-ups that might have enveloped the entire area. A major earthquake is recorded in Israel in 31 BC, being the oldest historically documented disaster in the region.
3. Historical Period (0 – 1,000 AD): low frequency of seismic activity. Nevertheless, quakes that did strike had devastating results in the entire Levant, as the earthquake of 749 AD can attest. That even quakes of 7.0 or higher on the Richter scale have left little evidence in the historical and archaeological records might be related to their epicentres being located at quite some distance from the DST or underneath the Mediterranean Sea, and/or originating so deep underground that not much of the tremor reached the surface. The geological sequence indicates mainly microscopically thin layers of disruption during that time period.
4. Modern Period (since 1,000 AD): active. Especially the last 500 years have been recorded as particularly active, with major earthquakes striking at a high frequency all across the region, notably in 1837 just north of the Sea of Galilee and 1927 at the northwestern end of the Dead Sea.

Geographical Pattern.
With a few exceptions, the epicenters of the matched earthquakes are situated very close to the
Dead Sea (within 150 km) or up to 500 km north of it along the DST. [Migowski et al. 2004: 312]

Again, this is a very rough summary. Consult the cited papers with bibliography for further details. The chronology does not reach as far into prehistory for this factor, as the sample data becomes less and less clear with the depth of the core. While I am uncertain about the significance of this pattern and how it came about, I believe it can help refute the arbitrary selection of individual quakes to create a pattern of choice across a vast chronological stretch.

1. prior to 1,050 BC: Epicentres are scattered along the DST fairly evenly. Several major quakes occurred to the south of the Dead Sea, but also in the north and towards southeastern Turkey.
2. 1,050 BC – 1,000 AD: Epicentres are located primarily along the northern segment of the DST, including the 749 AD quake.
3. 1,000 – 1,600 AD: Epicentres are scattered along the DST fairly evenly.
4. 1,600 – present: Epicentres are located primarily along the northern segment of the DST. The last few small tremors all fall within this pattern, including the major quakes of 1837 and 1927.

I’m the first one to say that this is not the most scientific of analyses of Levantine earthquakes during the Holocene. But Marco Shmuel of Tel Aviv University (whose analysis of the 749 AD quake I have cited above) has decided to select 4 large and notable quakes of the last two thousand years to make up a chronological pattern that has little grounding in reality, in my opinion. He selected:

* 31 BC: western Jordan Valley. Magnitude: 6.7. Massive geological impact. Occurred during a moderately active seismic period that was focussed on the northern part of the DST.
* 363 AD: northwest of the Sea of Galilee. Magnitud: 6.7. Geological impact unknown (historical source only). Occurred during a period of low frequency activity that was focussed on the northern part of the DST.
* 749 AD: northern Jordan Valley. Magnitude: 7.0 – 7.5. Low geological impact (thin disturbance layer). Occurred during a period of low frequency activity that was focussed on the northern part of the DST.
* 1033 AD: southwest of the Sea of Galilee. Magnitude: 7.1. Massive geological impact. Occurred in the transition to the more active modern period during a time of even spread of the tremors along the DST.

Notice how all of these earthquakes originated in Israel, despite having had an impact throughout the region. Notice how he also leaves out the massive quakes of 1837 and 1927, even though both of these were located in Israel or very, very close to it. The same goes for a number of other quakes throughout the Middle Ages.

-> “So roughly, we are talking about an interval of every 400 years,” Marcos said. “If we follow the patterns of nature, a major quake should be expected any time because almost a whole millennium has passed since the last strong earthquake of 1033.”

–> “There’s been no release of tension, just buildup. It’s like if you have a strip of rubber between your hands and keep pulling it – you know that it’s going to snap eventually.”

MapYet the series of small earthquakes around the Dead Sea recently presents exactly that – a release of tension. Maybe not to the extent that a major quake can be prevented; maybe the small quakes are even a sign of a bigger one to come. We are in a seismically active period of the DST at the moment, and it is not unlikely that one will occur within the next few decades; after all, the current pattern suggests an average frequency of about 100 years between major quakes. The 400-year pattern suggested by Marco is an arbitrary number with little grounding in geological and even statistical fact that will do nothing but increase hysteria and fear – especially since most of the quotations of Marco’s predictions are accompanied by apocalyptic Bible verses indicating the return of the Messiah:

On that day his feet will stand on the Mount of Olives which lies to the east of Jerusalem, and the Mount of Olives will be split in half from east to west, leaving a great valley. Half the mountain will move northward and the other half southward.

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