Morocco earthquake movement drawn from space
- Written by Jonathan Amos
- Science Reporter
Satellites are rapidly mapping Morocco in the wake of Friday’s catastrophic 6.8-magnitude earthquake.
The information they collect will be vital for responders trying to reach affected towns and villages in the High Atlas Mountains.
Precise orbital images will tell them where infrastructure suffered the worst impacts — not just buildings but roads and bridges as well.
Relief workers have to cope with landslides. Satellite images can show them how to avoid blocked roads.
In addition to traditional visual data from satellites, other types of analysis are becoming available.
The map at the top of this page reveals how the Earth reeled in response to the massive energies released on Friday.
This is based on observations of the European Union’s Sentinel-1a satellite, around 06:30 GMT on Monday, as it passed north to south over Morocco at an altitude of 700 kilometers (435 miles).
Sentinel carries a radar instrument capable of sensing the ground in all weather conditions, day and night.
It routinely surveys earthquake-prone areas of the world, tracking what are often very subtle changes in elevation at the surface. But, of course, the changes that occurred on Friday were not subtle at all.
Researchers use interferometry to compare “before” and “after” views:
- The blue colors on the map show the upward movement of the ground – the ranger sees this as a shortening of the distance between it and the surface
- The yellow/orange colors show where the Earth has landed since the last time the European spacecraft measured the distance
The largest single movement toward the satellite reached 15 cm (6 inches). The maximum drop was about 10 cm (4 in).
But these are not exact changes in elevation, because the guard is looking at the ground from an angle. Therefore the maximum vertical deformations on the surface will be slightly larger.
From this type of analysis, scientists can confirm that it was a thrust fault buried to the north that caused the earthquake:
- It was “buried” meaning the rupture did not go all the way through the upper layers of rock to the surface
- “North dipping” tells us the direction of the rift – if a ball is placed on the rupture, it will roll north
“The fault plane dips to the north of the gap between the blue and yellow spots on the map,” says Professor Tim Wright, from the University of Leeds.
“The level gets deeper as you go below the blue zone. In geology, we call the part above the fault level the ‘hanging wall’ and we get more movement in this than the part below the fault level, which we call the ‘footwall.’
Scientists will use interferometric analysis like this to try to understand the earthquake and future hazard risks.
This is important because this particular area has not experienced a major earthquake in a very long time.
In the past, to gather the same information that Sentinel provides now, geologists would put on their boots and go inspect the ground.
“Go back to 1980, and the very large – magnitude 7 – Idhan earthquake – in Algeria, and it took very extensive field work to prove that the earthquake was the result of a buried thrust fault system,” Professor Wright says.
Now the UK’s Center for Monitoring and Modeling of Earthquakes, Volcanoes and Tectonics (COMET), which he directs, can automate the type of analysis described above, outputting interferometric maps within hours from the Sentinel Bridge.