Improving Physics‐Based Aftershock Forecasts During the 2016–2017 Central Italy Earthquake Cascade

Abstract

The 2016–2017 Central Apennines earthquake sequence is a recent example of how damages from subsequent aftershocks can exceed those caused by the initial mainshock. Recent studies reveal that physics‐based aftershock forecasts present comparable skills to their statistical counterparts, but their performance remains a controversial subject. Here we employ physics‐based models that combine the elasto‐static stress transfer with rate‐and‐state friction laws, and short‐term statistical Epidemic Type Aftershock Sequence (ETAS) models to describe the spatiotemporal evolution of the earthquake cascade. We then track the absolute and relative model performance using log‐likelihood statistics for a 1‐year horizon after the 24 August 2016 Mw = 6.0 Amatrice earthquake. We perform a series of pseudoprospective experiments by producing seven classes of Coulomb rate‐state (CRS) forecasts with gradual increase in data input quality and model complexity. Our goal is to investigate the influence of data quality on the predictive power of physics‐based models and to assess the comparative performance of the forecasts in critical time windows, such as the period following the 26 October Visso earthquakes leading to the 30 October Mw = 6.5 Norcia mainshock. We find that (1) the spatiotemporal performance of the basic CRS models is poor and progressively improves as more refined data are used, (2) CRS forecasts are about as informative as ETAS when secondary triggering effects from M3+ earthquakes are included together with spatially variable slip models, spatially heterogeneous receiver faults, and optimized rate‐and‐state parameters. After the Visso earthquakes, the more elaborate CRS model outperforms ETAS highlighting the importance of the static stress transfer for operational earthquake forecasting.

Stress Transfer From Opening Hydraulic Fractures Controls the Distribution of Induced Seismicity

“…Elastic stress change models have been used for decades to determine the triggering mechanism of tectonic earthquakes (Stein, 1999;Harris, 1998;Steacy et al, 2005;Meier et al, 2014;Wedmore et al, 2017), illuminating the sometimes unexpected spatiotemporal patterns which occur during seismic sequences. These models are regularly applied in physics-based earthquake hazard forecasts, using the observed slip on faults 10.1029/2019JB018794 to model the spatial distribution of subsequent, potentially damaging, earthquakes (Cattania et al, 2018;Mancini et al, 2019). Elastostatic modeling has also been applied with tensile sources, such as the analysis by Green et al (2015) of a seismic sequence associated with dyke intrusion in Iceland.…”

On the Use of Receiver Operating Characteristic Tests for Evaluating Spatial Earthquake Forecasts

“…This is not surprising given the complexity of the rupture and the surrounding fault network, as well as viscoelastic effects as highlighted by Chan and Stein (2009), who find a better correlation through careful consideration of the heterogeneous stress regime and regional fault network. Indeed, operational Coulomb forecasts can only compete with statistics‐based, all‐positive models when secondary triggering effects are included together with spatially variable slip models, and spatially heterogeneous receiver faults (e.g., Mancini et al, 2019, 2020).…”

Short-Term Foreshocks as Key Information for Mainshock Timing and Rupture: The Mw6.8 25 October 2018 Zakynthos Earthquake, Hellenic Subduction Zone

“…To test further this suggestion, we performed Coulomb Stress Change (CSC) modeling which has been extensively used as physics-based tool for aftershock forecasts, e.g., [ 122 , 123 ]. CSCs were calculated based on the complex slip distribution of the Zakynthos mainshock rupture at several depths (5, 10, 13, 15 km) and using the code Strop [ 124 ] in an elastic half-space [ 125 ].…”