Major Earthquake Shakes the South China Sea

The earthquake's significant depth is a key factor in understanding its impact and geological context. While shallow earthquakes can cause significant damage due to intense shaking, the deep location of this quake meant that the shaking was less intense at the surface.

Deep-focus earthquakes, occurring at depths between 300 and 700 kilometers, are often associated with subduction zones, where one tectonic plate is forced beneath another. In this case, the earthquake occurred in a region with a complex history of subduction, including remnants of the Neotethys Ocean and potentially the Proto-South China Sea.

Seismic tomography, a method of imaging the Earth's interior using seismic waves, reveals the presence of deeply subducted slabs in the area. These slabs are remnants of ancient tectonic plates that sank into the mantle. The extreme pressures and temperatures at these depths can cause minerals to undergo phase changes, which may trigger earthquakes through a process called transformational faulting.

The location of this earthquake near known subduction zones suggests it is related to the ongoing tectonic activity in the region. The USGS rated the likelihood of casualties or damage as low, and the U.S. Tsunami Warning Center did not issue an alert, saying the depth of the quake meant tsunami activity was not expected.

What caused this earthquake?

The earthquake was likely caused by transformational faulting within a deeply subducted slab, a remnant of an ancient tectonic plate in the Earth's mantle.

Why was the earthquake felt so far away?

The great depth meant that shaking intensity decreased only gradually with distance. A site located right above the epicenter is 620 kilometers away from the hypocenter (vertically). A site located two hundred kilometers away from the epicenter is still just 650 kilometers away from the hypocenter.

Was there a tsunami warning issued?

No, the U.S. Tsunami Warning Center did not issue an alert because the depth of the quake meant tsunami activity was not expected.

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