Seismic Activity in California’s Long Valley Caldera

October 25, 2023

Caltech researchers have employed cutting-edge imaging techniques to investigate heightened seismic activity in California’s Long Valley Caldera, a dormant supervolcano. Scientists have been monitoring this region within California’s Eastern Sierra Nevada mountains since the 1980s, where they have observed periods of significant unrest characterized by earthquake swarms and ground inflation, with the ground rising nearly half an inch annually during these episodes.

Unveiling the Depths

The researchers from Caltech have now unveiled the most detailed underground images ever captured of the Long Valley Caldera, penetrating up to 10 kilometers into the Earth’s crust. This groundbreaking research, led by Professor Zhongwen Zhan, was published in the journal Science Advances on October 18.

Understanding the Risks

While the region may not be gearing up for another supervolcanic eruption, the cooling process could release enough gas and liquid to trigger earthquakes and minor eruptions. He points to the example of May 1980 when the region experienced four magnitude 6 earthquakes.

Solidified Magma Chamber

The high-resolution images reveal that the magma chamber beneath the supervolcano is covered by a solidified lid of crystallized rock, a result of the cooling and solidification of liquid magma.

Imaging the Subsurface

To produce these underground images, the researchers inferred information about the subsurface environment by measuring seismic waves from earthquakes. Their technique involved the use of fiber optic cables, similar to those used for internet services, to make seismic measurements through distributed acoustic sensing (DAS). The 100-kilometer cable they employed for imaging the Long Valley Caldera was equivalent to a stretch of 10,000 single-component seismometers. Over 18 months, the team recorded data from more than 2,000 seismic events, most of which were too small to be felt by humans.

A Technological Milestone

This research represents a groundbreaking achievement as it marks the first time that such deep, high-resolution images have been produced using DAS. Previous imaging from local tomography studies had been limited to the shallow subsurface environment at depths of about 5 kilometers or covered larger areas in lower resolution.

Future Explorations

The team’s future plans involve using a 200-kilometer cable to delve even deeper into the Earth’s crust, reaching depths of around 15 to 20 kilometers. This endeavor aims to gain further insights into the caldera’s magma chamber, often referred to as its “beating heart,” as it continues to cool. Such technological advancements hold promise for enhancing our understanding of crustal dynamics in other regions as well.

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