Non-volcanic tremor driven by large transient shear stresses.

Area of Science:

• Geophysics
• Seismology
• Tectonophysics

Background:

• Non-impulsive seismic radiation, or tremor, is observed at volcanoes and subduction zones.
• The exact cause of non-volcanic tremor remains unclear, with fluid movement and plate interface slip as leading hypotheses.
• Previous studies in Japan linked tremor to low-frequency earthquakes and shear slip on the subduction interface.

Purpose of the Study:

• To investigate the cause of non-volcanic tremor in the Cascadia subduction zone.
• To determine if external seismic events can trigger tremor.
• To understand the relationship between tremor, slow slip events, and plate interface stresses.

Main Methods:

• Analysis of seismic tremor data from the Cascadia subduction zone.
• Correlation of tremor bursts with seismic wave arrivals from the 2002 Denali, Alaska earthquake.
• Calculation of shear stresses on the plate interface based on Love wave displacements.

Main Results:

• Identified tremor bursts in Cascadia triggered by Love waves from the Denali earthquake.
• Tremor occurred during specific Love wave displacements, indicating a triggering mechanism.
• Calculated shear stresses of approximately 40 kPa, suggesting very low effective stress on the plate interface.

Conclusions:

• Tremor and potentially slow slip events can be instantaneously induced by shear stress increases on the subduction interface.
• This phenomenon represents a frictional failure response to increased driving stress.
• The findings challenge existing models and highlight the sensitivity of subduction zones to external stresses.