The slip budget at a subduction zone megathrust is met by a spectrum of slip behaviors including coseismic slip from great earthquakes, afterslip, episodic tremor and slip (ETS), long‐term slow slip events (SSEs), and quasisteady interseismic creep. Long‐term geodetic monitoring at the Nankai subduction zone in southwest Japan has recorded deformation observations spanning nearly a complete earthquake cycle, making this region the best study area for obtaining a full understanding of how the slip budget is partitioned along the interface and how the rheological conditions evolve through space and time. In this work, we conduct an iterative inversion of vertical surface displacement data to jointly estimate coseismic slip during the 1944/46 Tonankai and Nankai earthquakes, spatiotemporal afterslip history following those earthquakes, and postseismic mantle flow. A suite of postseismic models with variable elastic slab and plate geometry and mantle viscosity all show at least 30 years of sustained afterslip within the ETS zone and the gap between the top of the ETS zone and the fully coupled zone. This result demonstrates that stable, long‐duration afterslip is possible in the ETS zone. Summing the estimated cumulative slip from this study with estimates from previous studies of cumulative slip during the interseismic period, including episodic SSEs, we find that eastern Shikoku island has nearly met all of its slip budget for a 150‐year interseismic cycle, whereas western Shikoku island has a slip deficit of nearly half the budget (4 out of 8.25 meters) above 20 km depth on the subduction interface.
While large earthquakes have been documented in stable continental regions, such as the central United States, they occur too infrequently to provide reliable observations of earthquake-related impacts. Using the state of Indiana as a case study, we investigate the impacts of five deterministic scenarios—three occurring outside the borders of the state and two within the state. They include a M7.3 Wabash Valley event in southern Illinois, a M7.6 New Madrid event in southeastern Missouri, a M6.2 event in west central Ohio, a M6.2 event near Evansville, Indiana, and a M5.8 Indianapolis event. The locations and magnitudes are based on known fault locations and credible interpretations of the earthquake history in the region. We use a combination of the US Geological Survey’s ShakeMap and the Federal Emergency Management Agency’s (FEMA) Hazus software packages to assess earthquake-triggered ground shaking and its effects on the built environment. We also use the United States Geological Survey (USGS) Ground Failure estimation tool to examine the spatial distribution of anticipated earthquake-induced landslides and liquefaction. The five main deterministic scenario models indicate that moderate-sized urban earthquakes may represent a greater threat to a state like Indiana than a large-magnitude event from the New Madrid seismic zone. To better understand the influence of earthquake source parameters on impacts, we conducted a sensitivity analysis for earthquakes near Indianapolis and Evansville, where we reviewed losses due to differences in magnitude, depth, strike, and dip. Based on the model projections, magnitude and depth have first-order and relatively predictable influence on losses. The orientation and dip of the causative fault in relation to populated areas can alter economic losses for an event of the same magnitude by 13%–32%. Deterministic scenario analyses, such as those presented here, can potentially be of widespread utility for understanding earthquake impacts in the central United States and other low-seismicity, stable continental regions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.