Diverse Behavior of Slow Slip and Tremor at the Northern Costa Rica Subduction Zone
Abstract
Several episodes of slow slip and tremor are believed to have occurred at the plate boundary in northern Costa Rica between 2000 and 2008. The evidence for these events varies and consists of: 1) correlated fluid flow excursions and seismic tremor recorded on ocean bottom instruments in 2000; 2) offsets in continuous GPS data in September 2003; 3) offsets in GPS data accompanied by seismic tremor in May 2007; and 4) strong prolonged seismic tremor in August 2008. Modeling of the 2000 event suggested that slip occurred at shallow depth, between the surface and ~15 kilometers. The much better constrained slip distribution of the 2007 event revealed 2 patches, the stronger centered at ~30 km depth, near the down dip transition from stick-slip to stable sliding, and the weaker patch located at ~6 km depth at the up dip edge of the shallow frictional transition. The 2003 event was recorded on too few instruments to be modeled. These results are significant in that they are the first to suggest that slow slip occurs at the up dip transition from stick-slip to stable sliding; locations of slow slip in other environments have been limited to the down dip frictional transition. Due to the relatively small surface displacements (1-2 cm) associated with Costa Rica slow slip events, the coincident occurrence of seismic tremor is important for their detection and study. Similar to tremor observations in southwest Japan, some Costa Rica tremor consists of swarms of low-frequency earthquakes that occur as repetitive stick-slip motion on the plate interface, contains very low frequency earthquakes, with dominant energy between 20-50 s, and appears to be tidally modulated. We discuss the diverse slow slip and tremor behavior observed in this subduction zone, explore its relationships and contrast it with other environments.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T21F..03S
- Keywords:
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- 1207 GEODESY AND GRAVITY / Transient deformation;
- 7215 SEISMOLOGY / Earthquake source observations;
- 7240 SEISMOLOGY / Subduction zones;
- 8104 TECTONOPHYSICS / Continental margins: convergent