[Rockhounds] Giant diamonds may hold the key to superdeep earthquakes

[Kreigh Tomaszewski]

Earthquakes shouldn’t occur more than 300 kilometers below Earth’s surface,
according to most geophysical models. Yet they commonly do—a phenomenon
that has mystified seismologists for decades. Now, researchers suggest
water carried by tectonic plates shoved beneath continents could be
triggering these deep temblors. The find may also explain another marvel:
why a huge number of fist-size diamonds form at this depth.

Earthquakes typically occur when the two sides of a fault, or the opposite
sides of a tectonic plate boundary, scrape past each other. But far beneath
our planet’s surface, the pressures are too high for such slippage, and
rocks are typically so hot they ooze and flow rather than break. That has
led geophysicists to come up with alternate explanations for deep seismic
activity, which can be very strong but largely too far away for us to feel.


One idea is that some minerals, under the extreme heat and pressure deep
within our planet, can suddenly lose volume, with the runaway collapse over
large distances causing strong quakes. A second notion is that once a quake
gets going—because of the sudden collapse of minerals or another
cause—rocks near the tip of the rupture heat up even further and weaken,
fueling the quake. A third cause might be water released from rocks deep
below Earth’s surface, which could weaken other rocks nearby, allowing them
to fracture more easily. Researchers have largely dismissed that
explanation, however, because it wasn’t clear where such water would come
from.

Steven Shirey, a geochemist at the Carnegie Institution for Science, had a
hunch: diamonds. The precious gems can accumulate layers as they grow,
gathering imperfections—such as flecks of surrounding rocks—as they get
bigger. Those so-called inclusions can also contain pockets of mineral-rich
water.

https://www.sciencemag.org/news/2021/06/giant-diamonds-may-hold-key-superdeep-earthquakes