Abstract
Abstract The aseismic slow slip event of 2001–2002 in Guerrero, Mexico, with an equivalent magnitude MW ~ 7.5, is the largest silent earthquake (SQ) among many recently recorded by GPS in different subduction zones (i.e. Japan, Alaska, Cascadia, New Zealand). The sub-horizontal and shallow plate interface in Central Mexico is responsible for specific conditions for the ~100 km long extended transient zone where the SQs develop from ~80 to ~190 km inland from the trench. This wide transient zone and relatively large slow slips of 10 to 20 cm displacements on the subduction fault result in noticeable surface displacements of 5–6 cm during the SQs. Continuous GPS stations allow one to trace the propagation of SQs, and to estimate their arrival time, duration and geometric attenuation. These propagation parameters must be accounted in order to locate source of slow slips events and to understand the triggering effect that they have on large subduction earthquakes. We use long-baseline tiltmeter data to define new time limits (onset and duration) for the SQs and continuous records from 8 GPS stations to determine the propagation of the 2001–2002 SQ in Central Mexico. Data from the CAYA and IGUA GPS stations, separated by ~170 km and located along the profile perpendicular to the trench, are used to determine that the surface deformation from the 2001–2002 SQ started almost instantaneously. It propagated parallel to the coast at ~2 km/day with an exponential attenuation of the horizontal surface displacement and a linear decrease of its duration with distance. Campaign data obtained yearly from 2001 to 2005 at the Oaxaca GPS network have been modeled according to a propagation of the 2001–2002 SQ step-like displacement anomaly. This modeling shows that the SQ ceased gradually in the central part of the Oaxaca segment of the subduction zone (west of Puerto Angel, PUAN) and then it apparently triggered another SQ in SE Oaxaca (between PUAN and Salina Cruz, SACR). The estimated horizontal velocities for inter-event epochs at each GPS site are used to assess an average interplate coupling in the Central Oaxaca subduction zone.
Highlights
This long-distance effect is attributed to the subhorizontal configuration of the subduction plate interface, which is partially coupled on its broad transition zone from the seismogenic locking to free slipping
The analysis of the long baseline tiltmeter (LBT) data shows that the duration time of 2001–2002 silent earthquakes (SQ) displacement recorded by the ACAP permanent GPS station is about two times longer than the most active phase of the anomalous displacement
This observation required a reevaluation of onset times at all GPS stations of the network “Simologia-UNAM”
Summary
Silent earthquakes (SQ) (see a classification of slow slip events by Kawasaki, 2004) in the subduction zones of Japan (i.e, Hirose et al, 1999; Ozawa et al, 2002; Sagiya and Ozawa, 2002; Sagiya, 2004), Cascadia (Dragert et al, 2001), Alaska (Freymueller et al, 2002), New Zealand (Beavan et al, 2003; Douglas et al, 2005), and Mexico (Lowry et al, 2001; Kostoglodov et al, 2003; Larson et al, 2004) are one of the most interesting observations in studies in the seismotectonics of subduction zones. Assuming that the 2001–2002 slow slip crustal deformation propagated into Oaxaca with a velocity and a duration-distance relation (both estimated through continuous GPS records), all five sets of campaign data (2001–2005) can be fit with a modeled step-like displacement signal at each GPS site. This procedure would provide some constrained (by onsets and durations) estimates of the amplitudes (U) of anomalous displacement during the SQ. The results of the same analysis applied to the time series from other permanent GPS stations can be found at http://laxdoru.igeofcu.unam.mx/∼ivonne/EPS1416
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
