Earthquake shaking intensity: toward robust geologic constraints

After more than a century of seismological observations, little data exists for the rare ground motions that recur at millennial scales, or the strongest ground motions that occur very near earthquake sources. Geologic data, including fragile geologic features (e.g., precariously balanced rocks, rock towers, speleothems) and other paleoseismic observations (e.g., landslides, turbidites, paleo liquefaction, and slickenlines), can provide insight into the intensity and spatial extent of past ground motions. The interpretation of these data is inherently multidisciplinary. Typically, geologic data must be dated and critical ground shaking intensities must be calculated prior incorporation into Probabilistic Seismic Hazard Analysis or comparison with earthquake simulations. This presentation will highlight several threads of active research. In the northeastern US, precariously balanced rocks are used to validate site-specific hazard curves and constrain the locations of cryptic earthquake-source faults. In southern California, observations of rock-tower seismic response improve fragility estimates. In the Pacific Northwest, rock tower and landslide data are combined to test the validity of megathrust ground-motion simulations. As methods continue to improve, geologic constraints on past shaking intensity will likely provide a unique insight into earthquake processes and hazards.

Speaker: Devin McPhillips, US Geological Survey

Attend in person or via Zoom (see weblink)