Don't blame the Trojan
Horse: Earthquakes toppled ancient cities, Stanford
geophysicist says
BY ELLEN LICKING
Around 1200 B.C., the
great Bronze Age civilizations of the Eastern
Mediterranean toppled like a string of dominos. One by
one, over a period of 50 years, dozens of bustling
centers of scholarship and industry, including Troy,
Mycenae and Knossos, collapsed into rubble. Today,
crushed skeletons and scattered debris are all that
remain of the powerful cities. What force could wreak
such widespread destruction?
Historians and
archaeologists have long battled over this question,
citing civil war, invasion and pestilence as possible
causes. When Stanford geophysicist Amos Nur examines the
evidence, he sees another possibility: The earth moved. A
string of massive earthquakes could have knocked down one
city-state after another, bringing the Bronze Age
civilizations to a premature end. Earthquake activity
also may be at the root of the biblical prophecy of
Armageddon, the site of the final conflict between good
and evil. According to Nur, the repeated destruction of
the city Megiddo probably inspired the author of
Revelation to script his haunting prediction of the
Apocalypse.
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For over 20 years, Nur has
been studying the role of earthquakes in the Eastern
Mediterranean. By poking around the ruins of Megiddo and
other ancient cities, he has gleaned fundamental
information about the patterns of large quakes. Amidst
the rubble of the ancients, Nur discovered clues that may
help modern geophysicists understand when and why
earthquakes occur. His findings suggest that earthquakes
are episodic periods of greater earthquake activity
are bracketed by periods of relative quiet. Large quakes
may trigger other large quakes, in a domino effect that
zips down a fault line, knocking down cities along the
way.
Nur is the Wayne Loel
Professor of Earth Sciences, director of the Rock Physics
and Borehole Project, and the current chair of Stanford's
geophysics department. He is an expert on the physics of
large-scale earth movements, including earthquakes. In
the early 1970s, he began studying the temporal and
spatial patterns of historical earthquakes in order to
identify indicators of future tremors. He chose the
Eastern Mediterranean, the Holy Land, since it has the
oldest, most complete record of earthquake activity.
"Although human history in this region provided
evidence for bygone earthquakes, it was recent advances
in our understanding of plate tectonics which imparted
unexpected insights about the destruction of ancient
cities," he said.
According to the plate
tectonics model, the crust, or outer layer of the earth,
consists of about a dozen large, irregularly shaped
plates that slide over, under and past each other. As the
plates move relative to each other, sudden dislocations
in segments of the crust create fractures, or faults.
Because faults reflect zones of weakness in the crust,
earthquakes tend to occur at the plate boundaries in
these regions. Those fault zones often form the mountain
passes and river valleys most used by humans in their
migrations.
For five millennia, the
city of Megiddo stood at one of the most important
junctions in the ancient Near East, the Nahal Iron Pass.
This pass was the only means of traversing the
Carmel-Gilboa mountain range on the road from Damascus to
Egypt. By controlling this route, Megiddo commanded the
course of trade and the march of armies in the Holy Land.
Excavations suggest the city was repeatedly devastated by
some large force. Archaeologists believe that warring
factions were responsible for this destruction. Nur is
certain that earthquakes were partly to blame.
Megiddo is located very
near the Carmel-Gilboa fault system, which is a branch of
the larger and more dangerous Dead Sea fault system. The
latter system accommodates motion between two plates, the
Arabian plate to the east and the Mediterranean plate to
the west. Given Megiddo's proximity to a fault zone,
"it is beyond doubt that Megiddo, along with its
neighboring territories, must have experienced
earthquakes strong enough to cause significant or total
destruction," Nur said.
Archaeological and
historical data support Nur's hypothesis. According to
written records, the Holy Land has been shaken by 11
devastating earthquakes since 1400 B.C. At Megiddo, three
layers of destruction cannot be explained by the invasion
of foreign armies. In addition, the excavation of sites
far to the north and to the south suggests that
additional cities were damaged at the same time as
Megiddo. This regional pattern of destruction is
consistent with a massive earthquake along the Carmel
fault.
The most compelling
evidence for Nur's earthquake hypothesis is also the most
gruesome: crushed skeletons found trapped under the
collapsed rubble. The tortured positions of the bodies
indicate that these people were struck by a sudden and
massive load. The amount of debris found in adjacent
areas suggests that the wall's collapse was not an
isolated incident. It is unlikely that these people died
in an invasion, given the presence of pottery shards and
precious metals in their immediate vicinity. Why would
conquerors destroy valuable objects instead of looting
them?
Also, there exists at
least one biblical reference to seismic activity at
Megiddo. John of Patmos, the author of the book of
Revelation, appeared to know of Megiddo's frequent
destruction by earthquakes when he wrote, "And they
assembled them at the place that in Hebrew is called
Armageddon and there came a violent earthquake"
(Revelation 16:16). The word Armageddon is a Greek
transcription of the Hebrew Har Megiddo, which
means the Mount of Megiddo. It seems likely that John
used the recurring desolation of this one particular city
to symbolize his vision of the Apocalypse to come.
Nur and his colleague,
Hagai Ron of the Israel Institute of Geophysics, reported
their data on Armageddon's earthquakes in the 1997
edition of the journal International Geology Review.
The fall of Troy
and more
Recently, Nur expanded his
geophysical analysis of the Holy Land to include cities
besides Megiddo. His current work suggests that
earthquakes may have played a large role in the collapse
of at least 50 great cultural centers, including Troy,
Mycenae and Knossos, at the end of the Bronze Age. He
presented his data in July at a conference on the
destruction of Bronze Age civilizations held at Cambridge
University.
Because it took 50 years,
from 1225 B.C. to 1175 B.C., for the major cultural
centers to collapse, it is unlikely that the end of the
Bronze Age was caused by a single historical event.
However, a string of earthquakes could have destabilized
society enough to wipe out the economic, social and
political structures. "The end of the Bronze Age may
actually have been a period of recovery following a
string of severe earthquakes," Nur said.
According to Nur, seismic
records indicate that large earthquakes are temporally
clustered. Short periods of very intense earthquake
activity are preceded and followed by long interludes of
relative quiet. Geologically, these episodes may be
explained as follows: When a plate ruptures in one place,
it strains another part of the plate boundary and may
cause its collapse a short time later. This cascade of
activity occurs until the entire plate boundary ruptures.
This period of intense activity is followed by longer
time periods when the whole plate is strained but doesn't
quite give. Eventually the strain builds up and the cycle
begins again.
Nur points to measurements
of Turkey's North Anatolian Fault as evidence of episodic
earthquake activity. In this century, between 1939 and
1967, a series of earthquakes ruptured the entire plate
boundary along Turkey's North Anatolian Fault, causing a
slip on the order of 2 to 4 meters. Historical records
indicate that seismic crises also occurred in the 4th and
8th centuries.
According to Nur, the
cities destroyed at the end of the Bronze Age were
located in regions that historically have experienced
high seismic activity. He has calculated the intensities
of recent earthquakes and shown that the modern-day
regions that experience heavy damage overlap with the
ancient ruins destroyed at the end of the Bronze Age. As
Nur states, "Earthquakes have been happening in this
region for thousands of years. There is no way that these
places could have escaped severe ground shaking. It is
impossible."
It is not too hard to
imagine how earthquakes might have caused the collapse of
ancient societies. Given their limited technology, it
would have been difficult for societies to rebuild their
magnificent temples and houses. In the wake of such a
catastrophe, skills like reading and writing could have
disappeared if people were concerned with more important
activities, like survival. "It probably took many
years to recover from such an event," Nur said.
Straining
geophysicists' ideas about quakes
Nur believes his studies
of the Bronze Age civilizations may cause geologists to
rethink the forces that generate earthquakes. Do
earthquakes really occur in episodic bursts? If so,
geologists will need to reevaluate how and when strain is
released along plate boundaries. The traditional view is
that strain is periodically released at each segment of
the plate boundary. The evidence obtained from Nur's
analysis of the Eastern Mediterranean suggests that
strain is released in episodes via a sequence of
earthquakes. A tremor at one segment of the plate
boundary appears to trigger a chain reaction of
displacements along the rest of the fault. According to
Nur, "The entire plate boundary gets unzipped by
this sequence of large earthquakes."
Nur's findings may have an
impact on the way geophysicists predict the likelihood of
future earthquakes. By charting past episodes of strong
earthquake activity, it may someday be possible to design
models that predict active and quiescent periods.
According to Nur, such predictive algorithms are a long
way off. He says, "Right now earthquake patterns
aren't regular enough to tell us anything."
Still, based on seismic
measurements, it's pretty clear that a strong earthquake
will hit the Eastern Mediterranean some time in the
future. Who knows? If John of Patmos' description is
correct, Megiddo may be the site of the "next big
one." As it was written in the Book of Revelation:
"into a place called Armageddon . . . there was a
great earthquake such as was not seen since men were upon
the earth. . . . And the great city was divided into
three parts, and the cities of the nation fell. . . . And
every island fled away, and the mountains were not."
SR
Ellen Licking is a
science writing intern at Stanford News Service.
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