Non-Volcanic Tremors in Costa Rica

Non-volcanic tremors were observed for the first time in Japan. They were also found at other subduction zones like in Cascadia, but also at transform faults like San Andreas fault. Intensity, duration and periodicity differ between the regions. In Cascadia the ocurrence of high non-volcanic tremor activity is related to silent slip events. Silent slip events in the region of Nicoya Peninsula, Costa Rica were observed by continious GPS measurements (Norabuena et al., JGR, 2004). In order to investigate a possible relation to non-volcanic tremor occurrence an array of 6 short period borehole stations was installed on Nicoya Peninsula, Costa Rica, since June 2006 as a part of the Collaborative Research Centre SFB 574 "Volatiles and Fluids in Subduction Zones". Within the first year of operation we observed non-volcanic tremor with a duration of 4 - 20 min and a frequency range of 1 - 5 Hz. A phase of increased activity took place between June and October 2007.