On the Relationship Between Offshore Geodetic Coverage and Slip Model Uncertainty: Analog Megathrust Earthquake Case Studies

Abstract

We apply a geodetic slip inversion technique to analog subduction megathrust earthquakes to demonstrate how limited offshore geodetic coverage affects coseismic slip models. We analyzed two archetypical megathrust earthquakes: trench‐breaking and non‐trench‐breaking earthquakes. Slip inversion models of analog earthquakes show quantitative and qualitative changes as a function of offshore coverage. Shallow slip cannot be resolved if the observation coverage of the offshore segment is <50%. Moreover, the slip pattern of shallow events flips from landward to trenchward skewed as offshore coverage reduces to <40%. The estimated slip for both event types converges to a similar unimodal pattern when there is no offshore coverage. We infer 5–20% slip overestimation when the observations are above the high slipping zone during trench‐breaking events versus 5–10% underestimation during non‐trench‐breaking events if observations are land limited. The moment magnitude derived for trench‐breaking ruptures might be significantly affected (ΔMw ~ 0.5).

Strain Signals Governed by Frictional‐Elastoplastic Interaction of the Upper Plate and Shallow Subduction Megathrust Interface Over Seismic Cycles

“…Seismotectonic Scale Modeling is a unique technique to forward model the tectonic evolution over seismic cycles (e.g., Rosenau et al., 2017, and references therein). The approach has been used to study the interplay between short‐term elastic (seismic) and long‐term permanent deformation (Rosenau & Oncken, 2009), earthquake recurrence behavior and predictability (Corbi et al., 2017, 2019, 2020; Rosenau et al., 2019), the linkage between offshore geodetic coverage and coseismic slip models (Kosari et al., 2020), and details of the seismic cycle (Caniven & Dominguez, 2021). Analog models are downscaled from nature for the dimensions of mass, length, and time to maintain geometric, kinematic, and dynamic similarity by applying a set of dimensionless numbers (King Hubbert, 1937; Rosenau et al., 2009, 2017).…”

“…Estimating the interseismic coupling is the foremost approach to evaluate the earthquake potential of subduction megathrusts (Chlieh et al., 2008; Métois et al., 2013; Moreno et al., 2010; Schmalzle et al., 2014; Wallace et al., 2012). While both updip and downdip limits of megathrust ruptures are typically located offshore and near the shore, respectively, centuries‐long recurrence intervals of the subduction megathrust earthquakes and geodetically insufficiently instrumented seafloors prevent us from achieving sufficient details of the shallow part of the megathrust (Kosari et al., 2020; Williamson & Newman, 2018). For instance, a weakly coupled interface had been predicted in NE Japan based on the incomplete and weakly constrained interseismic geodetic measurements before the 2011 Tohoku‐Oki megathrust event (Loveless & Meade, 2011).…”

“…This method has been used to study the interplay between short‐term elastic (seismic) and long‐term permanent deformation (Rosenau & Oncken, 2009). For mimicking the megathrust seismic cycle and its associated surface deformation, we use a zone of velocity weakening (stick‐slip) material and an elastoplastic wedge while the wedge is continuously compressed via a basal conveyor belt (Kosari et al., 2020; Rosenau et al., 2019). A stereoscopic image correlation technique has been used to monitor the surface deformation of the analog model (Adam et al., 2005).…”

Empirical Analysis of Global-Scale Natural Data and Analogue Seismotectonic Modelling Data to Unravel the Seismic Behaviour of the Subduction Megathrust

“…-Laboratory geodetic monitoring: models are monitored via cross-correlation of images of the top or side surfaces or the interior of the model (e.g., with the Particle Image Velocimetry, PIV method; Sveen 2004). Applied to the top surface this technique is equivalent to having a dense network of continuous GPS stations (hence the name "laboratory geodesy models") which allow inverting for relevant earthquake source parameters (e.g., Rosenau et al, 2019;Corbi et al, 2013;Kosari et al, 2020).…”

“…The process of earthquake synchronization is one of the key aspects in seismogenesis and is considered responsible for the origin of megaearthquakes unzipping large parts of a subduction zone. Nowadays, analog models are also used for testing earthquake predictability (e.g., Corbi et al, 2019) and for identifying optimal geodetic configurations for monitoring convergent margins (Corbi et al, 2020;Kosari et al, 2020).…”