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Cover Story

Imaging Israel’s Dead Sea Fault to Understand How Continents Stretch and Rift

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An international team of scientists collaborated last April to image the deep structure of the Dead Sea fault in Israel. Their findings will help show how tectonic-plate motion deforms continental crust and will improve understanding of earthquake hazards and natural resources along the fault.

Photo of the research vessel in calm water in the foreground, with hills in the background
Above: The Israel Oceanographic and Limnological Institute research boat Lillian on its way to deploy receivers in the Sea of Galilee to record data during the April experiment. Photo credit: Uri ten Brink, USGS [larger version]

Like California’s San Andreas fault, the Dead Sea fault is a transform plate boundary, along which two tectonic plates slide past one another. It separates the Arabia plate from the Africa plate (see map). The fault’s path through Israel is marked by a valley approximately 20 kilometers (12 miles) wide, underlain in places by deep subsurface sedimentary basins, giving rise to the name “Dead Sea Rift.”

Graphic map explaining Earth's crustal plate boundaries
Above: Generalized plate boundaries from This Dynamic Planet (USGS, 2006). Red lines are spreading boundaries, where new crust is generated as plates move away from one another; black lines are transform faults where plates slide past one another. Black lines with sawteeth are convergent boundaries, where one plate dives beneath another in direction of sawteeth. Hatched red lines are broad belts of deformation. Red dots are hotspots, where material from the Earth’s mantle wells up into the crust. [larger version]

Many transform plate boundaries are on the seafloor, where they connect segments of mid-ocean spreading ridges. The San Andreas and Dead Sea faults, in contrast, are on continents and cut through the entire lithosphere (the top approximately 100 kilometers [60 miles] of the Earth). Thus, they provide a window into how the continental crust and upper mantle get deformed by the relentless movement of tectonic plates. The Dead Sea fault gives a somewhat clearer view than the San Andreas fault, which is located over an old subduction zone and cuts through rocks with a complex past.

“The geological history and crustal structure of the Dead Sea area are simpler than those in California,” says Zvi Ben-Avraham, professor at Israel’s University of Haifa and co-supervisor of the April experiment. “We can more readily resolve the configuration of the plate boundary in the Dead Sea Rift, and then project it to similar tectonic environments around the globe.”

USGS research geophysicist Nathan Miller, a participant in the experiment, adds: “Sedimentary basins [low areas where sediment accumulates] along the Dead Sea fault serve as compact laboratories where we can examine continental stretching and rifting.”

Investigating this plate boundary has more than academic value: the Bible and historical and archeological records document numerous earthquakes along the Dead Sea fault. The largest to strike Israel in recent history was the magnitude 7.1 Safed earthquake, which occurred on January 1, 1837, killing more than 5,000 people and causing massive damage to cities and villages. Enhanced understanding of the fault will improve assessments of the hazards it poses. A more detailed picture of its structure can also help identify resources like oil and water, which are commonly stored in reservoirs of sedimentary rocks along such plate boundaries.

The recent experiment ran from April 8 to 12, 2018, and focused on the Sea of Galilee in the northern part of the Dead Sea Rift, where the researchers expected the crust to be different from previously explored areas to the south. To image the fault structure here, they used seismic (sound) energy generated by 12 underground explosive shots, 300–400 kilograms (approx. 700–900 pounds) each, along an east-west and a north-south profile (see map below). The sound waves penetrated as deep as 30 kilometers (20 miles) beneath the surface, bending and reflecting as they hit rock layers with different properties. The return signals were recorded by 550 receivers arranged at 200-meter (650 foot) intervals along the two profiles.

Graphic map showing study area with data collection and explosion sites marked; and including inset of larger area
Above: Study area. Green dots (locations of receivers) delineate profiles along which the international team collected data about the Dead Sea fault’s subsurface structure. Red triangles are where explosive shots were detonated to provide seismic (sound) energy for the experiment. Red fault strands reflect the complexity of the Dead Sea fault in this area. P.A., Palestinian Authority. [larger version]

The scientists buried most of the receivers a few centimeters below the ground surface. They modified 40 of the receivers to record data in the Sea of Galilee by housing them in water-tight flotations anchored to the lake’s bottom and replacing the geophones with hydrophones (microphones designed to work in water). The April deployment was the first test of this novel modification of land receivers for underwater work. It appears to have succeeded and will likely be used in future seismic data collection in estuaries and lakes.

Photo of 2 men kneeling on the ground over a shallow hole with a piece of equipment in it Photo of floating seismic receiver near the side of the research vessel
Above: Guy Lang, a Ph.D. student at the University of Haifa, installs a seismic receiver along the east-west profile. Photo credit: Uri ten Brink, USGS. [larger version]

  Above: One of 40 seismic receivers modified to work in water and anchored to the bottom of the Sea of Galilee. Photo credit: Uri ten Brink, USGS. [larger version]

In addition to imaging the structure of the Dead Sea fault, the receivers recorded nearby mining explosions and local earthquakes during the 2 days of deployment; these data will be included in the analysis. The controlled explosive shots detonated for the study were also used to calibrate local seismic networks and to study the ground’s response to shaking in Israel, Jordan, and the Palestinian Territories.

Photo of 2 men pouring pink powder into a hole in the ground
Above: Contractors pour explosive powder into one of the holes where shots were detonated to provide seismic (sound) energy for the experiment. See study area map for shot locations. Photo credit: Uri ten Brink, USGS. [larger version]

The participants came from the University of Haifa (UH), Israel; the USGS; and the Geophysical Institute of Israel (GII). The experiment was funded by the Richard Lounsbery Foundation and by the Israel Ministry of Energy and Infrastructure. Equipment and technical support were provided by The Incorporated Research Institutes for Seismology (IRIS) Portable Array Seismic Studies of the Continental Lithosphere (PASSCAL) Instrument Center in Socorro, New Mexico. The experiment was supervised by Uri ten Brink (USGS) and Zvi Ben-Avraham (UH), coordinated by Eldad Levi (GII), and conducted by Nathan Miller (USGS), Lloyd Carothers (IRIS-PASSCAL), Steve Harder (University of Texas at El Paso), students from the UH, and field crews from GII, and the Israel Oceanographic and Limnological Institute (IOLR).

Photo of 2 men looking at something on a table in the background, with chests of equipment in the foreground
Above: Working in a temporary lab in Kibbutz Moran, Lloyd Carothers (left, IRIS-PASSCAL) and Eldad Levi (Geophysical Institute of Israel) download data from seismic receivers (in blue and yellow boxes) retrieved after completion of the experiment. Photo credit: Uri ten Brink, USGS. [larger version]

The successful completion of this experiment on a tight schedule required a high degree of coordination among the field crews, drillers, and explosive experts, as well as coordination with police, military, and civil defense authorities. Data are currently being processed and analyzed at the USGS. A copy of the data has been archived with IRIS-DMC.

Preliminary examination of the data shows sound-wave returns from the top 10 kilometers (6 miles) of rock beneath the seafloor, and some reflections from deeper in the crust. In addition to images of rock deformed by faults and folds, some of the data will help the researchers determine the rock composition under the survey profiles. Stay tuned!

Related Sound Waves Stories
Expedition along a Hazardous, Fast-Moving Fault off Southeast Alaska—the Queen Charlotte-Fairweather Fault
Jan. 2018
Striking New Seafloor Imagery of the Queen Charlotte-Fairweather Fault in the Gulf of Alaska
Jan. - Feb. 2017
Mystery Gap: Connecting Earthquake Faults near San Francisco, California, Requires Many Approaches
Jan. - Feb. 2017
Investigating the Offshore Queen Charlotte-Fairweather Fault System in Southeastern Alaska
Dec. 2015 - Jan. 2016

Related Websites
Portable Array Seismic Studies of the Continental Lithosphere
Geography of the Middle East
Incorporated Research Institutions for Seismology
Israel Oceanographic and Limnological Institute

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Cover Story Imaging Israel's Dead Sea Fault to Understand How Continents Stretch and Rift

News Brief
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Field Work
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Scientists Who Assess Coastal Flooding Threats Receive Leadership Award

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Fulbright Scholar Joins Marine Geohazards Project in Woods Hole

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