Nature of asperities and barriers along the Chilean megathrust unveiled by an integrated analysis of seismicity, gravity, geodetic locking and wedge geometry

Asperities inside the seismogenic zone of subduction megathrust are regions where specific frictional properties allow a stick-slip behavior characterized by the accumulation of slip deficit over decades to centuries and its sudden release during earthquakes. Despite its major role on the occurrence of the most devastating earthquakes and tsunamis on the planet, the physical nature of asperities and their limiting barriers is still unclear. This is partially due to an, often, ambiguous interpretation of individual geophysical proxies that are theoretically connected with the frictional structure of the megathrust at quite different time scales, ranging from 10⁰-10² yrs (seismicity patterns, geodetic locking, Vp/Vs and MT anomalies) to 10⁵-10⁷ yrs (coastal geomorphology, forearc wedge geometry and associated basal friction, magnetic and gravity anomalies). If transient phenomena, like slow slip events (SSEs) or stress shadows created by previous earthquakes, do not dominate the seismogenic behavior of the megathrust, then short- and long-term frictional proxies should coincidently illuminate the location of asperities and barriers. Moreover, this would imply that the nature of this features must be connected to the geology structure of both converging plates, with strong implications to seismic hazard assessment. A number of previous studies have explored a combination of several geophysical proxies for megathrust frictional structure, most of them along the Chilean margin. Here we expand over the work of Molina et al. (2021) and Sippl et al. (2021) by performing an integrated analysis of gravity anomalies, friction from critical wedge theory, geodetic locking and seismicity patterns for the entire 4000-km long Chilean megathrust. Particularly, we use available (micro)seismicity catalogues to compute maps of the b-value of the frequency-magnitude relationship. This parameter contributes with an independent short-term proxy for the stress state of the megathrust and we treat it as an additional continuous field into a principal component analysis (PCA) similar to Molina et al. (2021) that aims to quantify the main spatial correlation between the proxies. We will also test other techniques to measure the degree of spatial correlation, like AI-based pattern recognition methods. This integrated analysis will also consider rupture length of historical earthquakes over the last 500 yrs and slip distribution of instrumental earthquakes and SSEs. This will allow us to test contrasting hypothesis about the nature of seismic asperities and barriers along the Chilean megathrust and elsewhere.