Earthquake Storms What triggered the collapse
It sounded like the roar of a high-speed train—but it caused far more devastation. The earthquake that hit northwestern Turkey at Izmit, near Istanbul, on August 17, 1999, measured 7.4 on the Richter scale and killed 17,000 people. The tremors destroyed entire buildings, collapsed bridges, burst dams and caused landslides. Three months later, another earthquake with a magnitude of 7.1 struck about 60 miles to the east.
Both quakes occurred on what is called the North Anatolian Fault, which runs across northern Turkey. Since 1939, a series of large earthquakes has worked its way roughly from east to west along the 650 miles of this fault line. Such an “earthquake sequence” occurs when the strain on a fault has accumulated gradually over a period of relative inactivity, sometimes lasting a few hundred years. This strain is then released in a series of earthquakes, each one triggering the next, rather than in a single large earthquake.
In earthquake sequences, the initial earthquake ruptures only a segment of the fault zone, thus putting more stress on an adjacent portion of the fault. The strain on this next section may then be released in a second earthquake. This could occur weeks, months, years or even decades after the first earthquake. This second earthquake puts additional stress on the next portion of the fault, forcing a third earthquake, and so on down the line until the entire fault is “unzipped” and free from strain. The strain along the fault line then begins to build up all over again—eventually, perhaps centuries later, leading to another stress-releasing earthquake sequence.
Earthquake sequences taking place in the medieval or ancient past are called “earthquake storms.” One such storm appears to have occurred between 350 and 380 A.D., damaging sites in Israel, Cyprus, northwest Turkey, Crete, Corinth, southern Italy, Sicily and northern Libya.
1 A longer earthquake storm, lasting more than 80 years, is thought to have occurred along the North Anatolian Fault from 967 to 1050 A.D., during which time more than 20 sizable earthquakes may have struck.
2We believe that an earthquake storm lasting 50 years, from about 1225 to 1175 B.C., substantially contributed to the collapse of Late Bronze Age civilization in the Aegean and eastern Mediterranean.
Nearly 50 Late Bronze Age sites in this region show evidence of catastrophic destruction, according to Robert Drews of Vanderbilt University. These devastated Late Bronze Age sites correspond very closely to sites struck by damaging earthquakes documented over the last century. These sites, it seems, have been earthquake-prone throughout history—and probably long before that.
3The precise cause of the death of the Bronze Age civilizations in the Aegean and eastern Mediterranean toward the end of the 13th century B.C. has long been a mystery. Scholars have proposed various diagnoses, including widespread drought, social unrest, external invasion and economic disaster. In 1948 Claude Schaeffer, the French excavator of Ugarit (modern Ras Shamra) on Syria’s Mediterranean coast, first suggested that an earthquake might have been responsible for the destruction not only of Ugarit but also of other Late Bronze Age sites. This idea was initially rejected, in part because the destructions at the end of the Late Bronze Age were spread over a 50-year time span and could not have been the result of a single catastrophe.
4 However, knowing today what Schaeffer could not have known in 1948, we suggest that one cause of this 50-year-long cataclysm was a series of earthquakes—an earthquake storm.
It is relatively easy for excavators to recognize destruction levels, but it is often difficult to determine their causes. Was it war, an accidental fire, an earthquake, a combination of events? A number of criteria suggest possible earthquake damage: collapsed, patched or reinforced walls; crushed skeletons, or bodies found lying under fallen debris; toppled columns lying parallel to one another; slipped keystones in archways and doorways; and walls leaning at impossible angles or offset from their original position.
5Archaeologists have found widespread evidence of earthquake damage like this dating to the crucial period, 1225–1175 B.C. In the Aegean, earthquakes probably struck at Mycenae, Tiryns, Midea, Thebes, Pylos, Kynos, Lefkandi, the Menelaion, Kastanas in Thessaly, Korakou, Profitis Elias and Gla. More sites could be added to this list, and, almost certainly, additional sites will be added as archaeological evidence accumulates. In the eastern Mediterranean, earthquake damage is visible at Troy, Karaoglun, Hattusa, Ugarit, Alalakh, Megiddo, Ashdod and Akko, among other sites.
6At Mycenae, for example, excavators found the wall flanking the entrance to the so-called Cult Center of the Citadel bulging outward, its roof slates fallen to the ground, and its stones charred by fire. Shortly after this destruction, new walls in the inner sanctum were built to prop up the original ones. One wall in a neighboring room was reinforced. New doors and windows were opened, and the original ones were walled up—all strong evidence of an earthquake.
7In the so-called Southwest House of Mycenae’s Citadel, the north and south walls of one room had collapsed, crushing a young man. The excavators found the skeleton under the burned debris. Huge pieces of plaster from the frescoes lining the walls of the building had fallen, apparently having come loose before the walls themselves collapsed.
8Amid the debris of Mycenae’s Panagia House I, excavator George Mylonas found a “skeleton of a middle-aged woman whose skull was crushed by a falling stone.” The body was then buried by material from the house, including smashed vessels and a chimney pot.
9 According to Mylonas, “House I was suddenly destroyed, but not by fire.” The piles of stones, the smashed vases with all their pieces, the crushed skeleton—“all seem to indicate that House I was destroyed by earthquake.”
10Klaus Kilian, the late excavator of Tiryns, long argued that the site was destroyed around 1200 B.C. by an earthquake that also affected other sites, such as Mycenae. The geoarchaeologist Eberhard Zangger has recently suggested that a catastrophic flash flood that buried Tiryns’s lower town about 18 feet deep may have been related to this earthquake.
11 The excavators of Midea, too, suggest that the destruction of the site toward the beginning of the 12th century B.C. was caused by an earthquake. As evidence, they point to the city’s “collapsed, distorted, curved and tilted walls,” as well as a skeleton found under the debris.
12Perhaps the most famous Late Bronze Age city showing evidence of earthquake destruction is Troy. Located in northwestern Anatolia, Troy lies near the western end of the North Anatolian Fault, not too far from where the devastating earthquakes of two years ago struck. Heinrich Schliemann, University of Cincinnati archaeologist Carl Blegen and other excavators at Troy have noted evidence of earthquakes in various occupational strata: Troy III (c. 2250–2050 B.C.), Troy IV (c. 2050–1950 B.C.), Troy V (c. 1950–1750 B.C.) and probably the great Late Bronze Age city of Troy VI (c. 1750–1250 B.C.).a This latter stratum may have been the city of Homer’s epics, which were written some four centuries later. Possibly, the city was severely weakened by an earthquake, making it susceptible to attack during the Trojan War.
Although some scholars dispute the idea that Troy was significantly damaged by an earthquake in 1250 B.C., the evidence for seismic destruction is powerful. Indeed, in their final report, the excavators of Troy VI write that they are confident “in attributing the disaster to a severe earthquake.”
13 Reexamining the remains, the geoarchaeologist George Rapp concluded that the “most tenable hypothesis for the cause of this destruction [Troy VI] lies in foundation failures stemming from earthquake-induced earth movements in the underlying unconsolidated materials. Interpreted thus, the evidence supplied by the Cincinnati excavators … seems overwhelming.”
14Cont'd next post.
