Séminaire ISTerre

---

Plate boundary transient slow slip events tracked by seismic tremors.

vendredi 28 mai 2021 - 11h00

Baptiste Rousset - ISTerre
--- 
Tectonic loading at plate boundaries is either released by fast seismic slip or by aseismic slip that can either be steady or transient. Continuous geodetic measurements during the past two decades is showing an increasing amount of transient aseismic deformation examples with various durations and spatial scales. Playing a key role in releasing part of the tectonic loading and in redistributing stresses on the plate interface, these slow transient slip events are crucial to be detected and analysed in detail. When accompanied by tectonic tremors, the seismic signals are providing important temporal and spatial information that should be accounted for.
In this presentation, I present two examples of using the seismic signal as a guide to extract the transient aseismic deformation signal from the geodesy time series. On the Parkfield segment of the San Andreas fault, tremors have been observed in the roots of the seismic zone. However, associated transient aseismic slip had never been detected. By using the timing of transient tremor activity and taking advantage of the dense Parkfield-area global positioning system (GPS) network with more than a decade of continuously recorded position time series, we are able to detect and characterize the moment of average deep slow slip events (SSEs) on the Parkfield segment. The detection is made using a geodetic matched filter approach in which post-processed GPS time-series stacked over 20 transient events are correlated with synthetic dislocation fault slip models. SSEs with an average moment equivalent to Mw 4.90 ± 0.08 at 16 km depth are releasing ∼ 25% of the loading rate during 5.5% of the interseismic time.
The other study considers a 5-year transient event occurring in Alaska. During this event, tectonic tremors are co-located with the inferred aseismic slip zone and occurred in weeks-long bursts of events. A decomposition of GPS time series relative to tremor times during the whole 5-year transient event shows that GPS site velocities are on average three to six times higher during tremor bursts than in between, suggesting that slip pulses are generally associated with tremor bursts. The dynamic modelling of a three-weeks subevent in September 2010 shows that both aseismic slip and the tremor front migrated along strike at speeds of ∼8 km/day and with slip rates of ∼3 mm/day. This particular slip pulse released 9% of the 5-year transient event total moment in 1.4% of its duration, proving the non-steadiness nature of slip rate during the 5-year deformation event. These two examples prove that combining geodetic and seismological recordings can help obtaining better temporal and spatial resolutions on transient aseismic slip models.

---

Equipe organisatrice : Ondes et structures

Séminaire uniquement en visio

Informations de visio :

https://univ-grenoble-alpes-fr.zoom.us/j/97295763658?pwd=Z0Y4OEJtNXFOMnRwcFlXNWl1eFpSQT09
Meeting ID : 972 9576 3658
Passcode : 783219