However this discrepancy in the depth of NVTs in those subduction zones may arise from the locating methods. 2005), Japan (Nugraha & Mori 2006) and Mexico (Payero etВ al.

2006 Ohta & Ide 2008), while in other studies it was proposed that they are located within the overriding plate like in Cascadia (Kao etВ al. Besides, some studies locate tremors at the plate interface as suggested in Japan (e.g. The authors suggest that long-term SSE could activate downdip short-term SSEs, which could remain undetected by GPS, and synchronized with NVT. Long-term SSEs are also observed in the Bungo Chanel in Southwest Japan and trigger neighbouring downdip NVT activity (Hirose etВ al. According to the classification proposed by Obara ( 2011), SSEs in Mexico belong to long-term SSE considering their duration and their updip position in the trench as shown by Vergnolle etВ al. However, the recent detection of NVT at the northern Hikurangi margin associated with the 2010 Gisborne SSE suggests that the thick accumulation of highly attenuating sediment in the accretionary wedge inhibits the NVT detection in some cases (Kim etВ al. 2007), even no NVT was observed during slow slip. 2009) and the Boso Peninsula of Japan (Ozawa etВ al. Moreover, in areas like the Hikurangi subduction margin, New Zealand (McCaffrey etВ al. 2010) the association of SSE and NVT does not seem systematic. 2006 Peterson & Christensen 2009) and Mexico (Payero etВ al. In other subduction zones like Costa Rica (Brown etВ al. For instance, in Cascadia and Southwest Japan subduction zones a clear temporal and spatial correlation between NVT and SSE has been observed and called episodic tremors and slip (ETS Rogers & Dragert 2003 Obara etВ al. The data acquired on these two geophysical processes reveal a wide diversity of behaviours that vary from one region to another. SSEs are usually accompanied by NVT episodes, which are weak seismic signals of long duration, persistent in time and coherent over many stations (Obara 2002 Rogers & Dragert 2003 Obara etВ al.

SSEs are transient aseismic slips that contribute to release the accumulated elastic strain at the plate interfaces. Non-volcanic tremor (NVT) and slow slip events (SSE) are observed in many active plate boundaries around the world (e.g. Wave scattering and diffraction, Rheology and friction of fault zones, Subduction zone processes 1 INTRODUCTION These observations suggest that both seismic velocity change and NVT can be used as indication of transient deformation at depth. We observe a correlation between velocity changes (for period band greater than 14 s) and tremor activity whereas no correlation exists between velocity changes and seismic noise energy measured at long periods. During the 2009вЂ“2010 SSE we measure NVT activity using continuous seismic records filtered between 2 and 8 Hz. The velocity changes can be interpreted together with other observables such as NVTs. This result is similar to what was observed during the 2006 SSE in the same region and suggests a non-linear behaviour of the crust. The comparison between the velocity changes and the deformation suggests that the velocity change is correlated with the strain rate rather than with the strain. Finally, we compute the transient deformation produced by the SSE in an elastic model using the slip evolution recovered from the inversion of continuous GPS. Below, the velocity perturbation increases with depth, affecting the middle and lower crust. No velocity change in the first 10вЂ‰km is detected. Then a linearized inversion of the velocity change measured at different period bands is applied in order to determine the depth of the portion of the crust affected by this perturbation. We analyse the velocity change at different period bands and observe that the velocity perturbation associated with the SSE maximizes for periods longer than 12 s. From a seismic array of 59 seismometers, installed in small antennas, we detect a velocity drop with maximum amplitude at the time of the first subevent. The 2009вЂ“2010 SSE presents a complex slip sequence with two subevents occurring in two different portions of the fault.

We test the sensitivity of the seismic velocity to strain variations in absence of strong motions. We use ambient noise cross-correlations to monitor small but reliable changes in seismic velocities and to analyse non-volcanic tremor (NVT) intensities during the slow slip event (SSE) that occurred in 20 in Guerrero.

State that seismac tremors