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Tidal modulation of nonvolcanic tremor.
Justin L Rubinstein1, Mario La Rocca, John E Vidale
1Department of Earth and Space Science, University of Washington, Box 351310, Seattle, WA 98195, USA. justin@ess.washington.edu
Science (New York, N.Y.)
|November 24, 2007
Summary
Nonvolcanic tremor and slow slip events in the Cascadia subduction zone are influenced by tidal forces. These seismic events occur on very weak faults, unlike normal earthquakes.
Area of Science:
- Geophysics
- Seismology
- Tectonics
Background:
- Nonvolcanic tremor and slow slip events are observed in subduction zones like Japan and Cascadia.
- These events differ from typical earthquakes in their source and scaling properties.
- Recent episodes in the Puget Sound/southern Vancouver Island region of Cascadia were well-recorded.
Purpose of the Study:
- To investigate the relationship between tidal forces and nonvolcanic tremor/slow slip events.
- To understand the factors controlling tremor genesis in the Cascadia subduction zone.
Main Methods:
- Analysis of seismic data from recent tremor episodes in the Cascadia subduction zone.
- Comparison of tremor pulsing periods with principal lunar and lunisolar tidal cycles.
Main Results:
- Tremor activity exhibited clear pulsing with periods matching lunar (12.4 hours) and lunisolar (24-25 hours) tides.
- Tidal stresses significantly influence tremor genesis more than normal earthquakes.
- Lithostatic stresses are orders of magnitude larger than tidal stresses.
Conclusions:
- The strong correlation suggests tidal stresses effectively trigger nonvolcanic tremor.
- Tremor likely initiates on extremely weak faults, as they are sensitive to small tidal stresses.
- This finding provides insights into the mechanics of slow slip events and fault behavior in subduction zones.
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