The Many Scales of Seismogenic Mass Wasting at Stratovolcanoes

Abstract:

Stratovolcanoes consist of some of the most unstable terrain in the world, and mass wasting processes are a major contributor to volcanic hazards. These hazards persist even during periods of volcanic quiescence and, unlike volcanic activity, events often occur without warning. Mass movements range in scale from small daily rock and icefall events to extremely rare sector collapses. Many events generate observable seismic waves that are frequently picked up by seismic networks at volcanoes. Seismic waves from surface events are different than those from earthquakes and are not nearly as well-characterized or understood. Traditional seismologic methods (e.g., location, magnitude) can rarely be applied, and therefore surface events are not often included in earthquake catalogs. For this reason, many investigations of seismogenic surface processes are limited to case studies of individual events and/or single event types. In order to improve our understanding of typical characteristics of different types of events, we have compiled a catalog of over 30 significant historical events (1997-present), mainly from North American stratovolcanoes, that were well-recorded seismically and also have complementary data. Event types range widely from outburst floods and debris flows/lahars to rock avalanches, rock falls, and dome collapses. We summarize the general seismic characteristics of each event type (e.g., frequency content, attenuation, duration, scaling relations, waveform patterns) and discuss the possibilities and limitations of how seismic recordings of surface events can be used to better understand the surface dynamics of volcanoes. Finally, we discuss what might be needed to institute surface event monitoring and/or early warning systems.