Washington: The twin earthquakes that struck north Venezuela last month shifted the earth almost two feet at some places, leading to massive devastation in Caracas and La Guaira, an analysis of data from the NISAR satellite has revealed. Researchers studied the images of the Earth taken by the NASA-ISRO Synthetic Aperture Radar (NISAR) satellite on June 13 and 18 (before the quake) and on June 25 and 30 to detect the changes in the terrain after the June 24 earthquake.
On June 24, a magnitude 7.2 earthquake struck northern Venezuela, followed by a magnitude 7.5 mainshock 39 seconds later. It killed more than 5000 and injured 16,700 while causing large-scale damage in Caracas and La Guaira. The states of Trujillo, Yaracuy, Carabobo, Aragua and Miranda had also been affected.
Scientists used a technique called InSAR, which compares data from repeat passes to detect subtle changes in the distance between the satellite and the ground, NASA said in a statement earlier this month.
This was the first time the NISAR urgent response system was used to map surface displacement from a large earthquake.
The fault is part of a network of fractures that lies along the boundary between the Caribbean plate to the north and the South American plate to the south.
Scientists say faults along this plate boundary, including the San Sebastian fault system, where these quakes likely occurred, and possibly part of the Bocono system, have long been accumulating strain.
The fault rupture propagated offshore, toward the east, and then back onshore near the international airport north of Caracas.
Just south of this fault section, along this part of the fault, the displacement was far greater than elsewhere, reaching as much as 60 centimetres (24 inches).
These are reasons why the damage in Caracas and La Guaira was so extreme, said Eric Fielding, a geophysicist at NASA’s Jet Propulsion Laboratory (JPL).
InSAR tells us a lot about what happened during this earthquake, he said.
According to NASA, NISAR views Earth at an angle, about 40 degrees from straight down, allowing it to capture a mix of horizontal and vertical displacement.
Using the NISAR data, the US Geological Survey refined its fault-slip model, or finite fault model, to better constrain how the fault slipped at depth, including along the rupture’s eastern section.
That is extremely helpful for the people who need to understand why the damage was so severe in that area, Fielding said.
The displacement maps for this event were provided through NISAR’s Urgent Response (UR) system, a fast-track process that can deliver data within 12 to 24 hours to support disaster response.
The rapid processing relies on predicted orbit information, so UR maps are preliminary until they are later reprocessed with precise orbit information, typically within a day or two.
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