From slow to fast, micro to macro, single events to cascades: A multi-scale study of seismic event triggering in lab and nature

For many decades, seismological research has progressively improved the image of earth structure using seismic waves. Yet the source of such waves - i.e. earthquakes - are not well understood. Recent improvements in seismic instrumentation and processing techniques have led to an unprecedented wealth of seismic records which allow us to study the mechanics of earthquakes with millimeter resolution. Taking advantage of these recent advances, my students, postdocs and I use laboratory experiments, numerical models and empirical observation to investigate fundamental problems in seismology such as: How do earthquakes start?; How do they stop?; What controls their magnitude? and; How do earthquakes interact?

Earthquakes rarely occur in isolation but rather as intertwined sequences of fore, main and aftershocks. Events within a seismic sequence are linked by a process that is often referred to as earthquake triggering. Triggered aftershocks are observed at many spatial and temporal scales and are thought to comprise 50 to 90% of the seismic record.

The NSF-career project will concentrate on a multi-scale investigation of seismic triggering and aftershocks in lab and nature. Investigations of triggering in controlled laboratory experiments have been complicated due to experimental and instrumental limitations. We will use newly-available high-speed, broad-band seismic instrumentation to record tiny seismic events during abrupt fault slip in the laboratory. Based on such records, we will advance the ability to identify conditions that amplify earthquake cascading processes.

The NSF-work will be conducted at the earthquake physics labs at GFZ-Potsdam, Germany and at the Center for Earthquake Research and Information (CERI). CERI provides an ideal environment for this research by bringing together diverse faculty, researchers and staff for excellent science and tech support. Using state-of-the-art seismic and optical imaging, the new lab at CERI is designed to image preparatory processes and earthquake cascades. The NSF-project is expected to improve the fundamental understanding of triggering processes and scale-invariant seismicity cascades in lab and nature. This work has the potential to transform strategies for earthquake hazard assessment and site-specific real-time aftershock forecasts.

In addition to the NSF-work, Dr. Thomas Göbel, assistant professor at the Center for Earthquake Research and Information (CERI) and UMRF Research Professor, and his research group are investigating human-induced earthquakes which occur as a by-product of hydrocarbon and geothermal energy production. A broader usage of geothermal energy has significantly been hampered (e.g., in Europe and South Korea) by unexpected earthquake activity during injection operations. To help mitigate induced seismic hazards, his research group is working with a geothermal operator in Nevada to monitor and understand the causes of induced earthquakes in geothermal fields, with support from the Department of Energy. The research has the aim to unravel fundamental processes that drive fluid flow and induced earthquakes to make geothermal energy production safer and more sustainable.

Göbel received the nationally competitive CAREER award and was recently recognized as a 2022 UMRF Research Professor for his research successes over the last year. His appointment will be effective September 1 and will last for two years.

For more information on his work, contact Göbel at thgoebel@memphis.edu.