In 2002 Alan Linde was elected a fellow of the American Geophysical Union. Over the years he has traveled to seismically active areas across the globe to install strainmeters — devices that detect small, long-term crustal movements — and other instrumentation. He and colleagues have deployed instruments in Iceland, in Peru, in China, along the San Andreas Fault in California, and beneath the ocean floor near the Japanese Trench.

This international team, aboard a ship near Japan in 1999, installed two packages of geological measuring equipment 1 km below the Pacific Ocean floor in waters 2 km deep. Team members from left to right are Ben Pandit, Alan Linde, Eiichiro Araki, Masanao Shinohara, Kiyoshi Suyehiro, Nelson McWhorter, and Selwyn Sacks.

Changes inside the Earth cause earthquakes, volcanoes, and other deformations on the surface of the planet. For a number of years, geophysicist Alan Linde, working with Department of Terrestrial Magnetism (DTM) collaborator Selwyn Sacks, has been involved in program to measure these disturbances in tectonically active areas around the world. The goal is to understand the processes at work at different depths in the Earth’s interior. Most of the data for this program have come from Sacks-Evertson borehole strainmeters—instruments developed at DTM that detect small, long-term crustal movements. Over the last few decades strainmeters have been installed in seismically active areas, including California, Japan, and Iceland. The high-resolution data have led to the detection of new processes, such as slow earthquakes in seismogenic zones — areas where earthquakes occur—and changes in magma reservoirs during episodes of volcanic activity.

Linde, Sacks, and colleagues from the Japan Meteorological Agency (JMA) are analyzing strainmeter data on the deformations caused by the 1986 eruption of Miharayama on the island Izu-Oshima in Japan. The instruments are part of a network installed by the JMA for its earthquake prediction research program. The data show that during the first stage of the eruption the relatively shallow reservoir — the ultimate source of magma for the eruption—was continuously replenished from much deeper source about 30 km below the surface. The scientists noted that the rate of replenishment changed at the time of small volcanic earthquakes. Strain changes preceding the second stage of the eruption were clear at depths to 50 km and came from the formation and propagation of dikes originating several kilometers below the surface. Surprisingly, most of the magma movement from the reservoir did not come to the surface but instead flowed into a large subterranean dike.

In 1999 Linde and collaborators installed borehole strainmeters, tiltmeters, and seismometers in drill holes about 1,100 meters below the ocean bottom near Japan. Data from these sites will provide new insights into the processes of plate motion and earthquake generation. The team has installed five new strainmeters in the San Francisco Bay area in a joint effort with the U.S. Geological Survey and the University of California at Berkeley and San Diego. A practical by-product of Linde’s science is the development of early warning systems for impending eruptions.

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