Do earthquakes large enough to collapse buildings and roads accompany volcanic eruptions?
Not usually. Earthquakes associated with eruptions rarely exceed magnitude 5, and these moderate earthquakes are not big enough to destroy buildings and roads.
The largest earthquakes at Mount St. Helens in 1980 were magnitude 5, large enough to sway trees and damage buildings, but not destroy them. During the huge eruption of Mount Pinatubo in the Philippines in 1991, dozens of light to moderate earthquakes (magnitude 3 to 5) were felt by several hundred thousand people. Many houses collapsed, but not primarily because of the shaking. Heavy ash from the eruption (made heavier by rain from a hurricane) accumulated on roofs and crushed them.
Stronger earthquakes sometimes DO occur near volcanoes as a result of tectonic faulting. For example, four magnitude 6 earthquakes struck Long Valley caldera, California, in 1980, and a magnitude 7.2 earthquake struck Kilauea Volcano, Hawaii, in 1975. Both volcanoes were quiet at the time. The Hawaii earthquake triggered a small eruption at the summit of Kilauea. No eruption occurred at Long Valley.
Learn more: Monitoring Volcano Seismicity Provides Insight to Volcanic Structure
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Listen to Earthquakes
Seismometers record vibrations from a wide assortment of ground motion events. Each event type has a distinctive ground-motion signal with unique frequency and amplitude—its own seismic signature. Seismologists are trained to identify the source of seismic events seen on a webicorder based on its ‘seismic signature’. Although most ground vibrations have a frequency too low
An Illustrated Guide to Reading a Seismogram
This video provides a tutorial for anyone interested in interpreting the seismic records on public webicorder displays.
Volcano Hazards
The United States has 169 active volcanoes. More than half of them could erupt explosively, sending ash up to 20,000 or 30,000 feet where commercial air traffic flies. USGS scientists are working to improve our understanding of volcano hazards to help protect communities and reduce the risks.
Video Sections:
- Volcanoes: Monitoring Volcanoes
Volcano Web Shorts 3: Seismology
USGS volcano seismologist, Seth Moran, describes how seismology and seismic networks are used to mitigate volcanic hazards.
Volcano Web Shorts 4 - Instruments
USGS technologist Rick LaHusen describes how the development and deployment of instruments plays a crucial role in mitigating volcanic hazards.
Damage from 2011 Virginia Earthquake
Photo of chimney damage at a house in Louisa County, Virginia. This was a result from a magnitude 5.8 earthquake in Virginia on August 23, 2011.
Northridge, CA Earthquake Damage
Collection of USGS still images taken after the January 17, 1994 Northridge earthquake highlighting the damage to buildings and infrastructure.
USGS volcano seismologist analyzes Mount Pinatubo seismicity
USGS volcano seismologist David Harlow conducts analysis of Mount Pinatubo seismicity.