Thorwart, Martin and Rabbel, Wolfgang (2012) Non-volcanic tremor in Costa Rica: b-values, moment release and tidal modulation. [Poster] In: The Lübeck Retreat, Collaborative Research SFB 574 Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters. , 23.-25.05.2012, Lübeck . The Lübeck Retreat: final colloquium of SFB 574; May 23-25, 2012: program & abstracts. ; p. 32 .

Abstract

Nicoya Peninsula (N Costa Rica) since July 2006 by using an array of short period borehole
seismometers. NVT hypocenters locate between 30 and 45 km depth near the interface of the
subducting Cocos and overriding Caribbean plates. They form a depth continuation of the
seismogenic zone. We present the results of a statistical analysis of the time series of NVT events
recorded continuously over the past 5 years. Using tremor time duration as a measure of their
magnitude we found that different scaling laws apply to different phases of NVT activity. Bursts
(swarms) of NVT events follow a Gutenberg-Richter type of law with a b-value of 1 if the cumulative
tremor duration of each burst is converted to seismic moment and earthquake magnitude by
application of corresponding empirical constants found for the Cascadia subduction zone (e.g. Wech
et al., 2010). However, the time length of single tremors follows a different statistics. It cannot be
characterized by a Gutenberg-Richter type relation but can be represented by two pairs of a,b-values
and a "corner duration time". These characteristic constants are different for the time intervals of
bursts and between bursts. This difference in the statistical behavior can possibly be explained by
tidal forcing of the tremor activity during burst phases: It was found that about 2/3 of the NVT events
belonging to bursts coincide with tidal stress maxima whereas no such correlation could be identified
for the time intervals between bursts.

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