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A New Intensity Data Set and Intensity Prediction Equation for Crustal Earthquakes in the Western United States

A new data set for macro intensity from crustal earthquakes in the Western US was developed combining the Did you feel it (DYFI) data set from the USGS with the historical intensity data set. Rupture distances were estimated for all events with magnitudes greater than 6. The site conditions are parameterized by the proxy-based VS30 and by the surface geology. The full data set includes 696,000 intensity observations from 5561 earthquakes. In addition to the intensity values, the data set includes the peak acceleration and peak velocity from the NGA-W3 data set for intensity observations near seismic stations. The data set is dominated by the DYFI observations with 96% of the intensity values and 98% of the earthquakes. For magnitudes of 6 or larger at distances less than 30 km, the historical intensity data accounts for 20% of the intensity values. To avoid the impact of censoring on lower MMI values, we establish (1) an Rmax distance based on the distance at which the minus two standard deviation level below the median from a non-parametric fit, and (2) all intensity values less than 2.1 were excluded. This reduced the data set used to develop the intensity prediction equation (IPE) to 358,000 recordings from 3642 earthquakes. The IPE is developed using model forms and regression methods commonly used in modern ground-motion models. In particular, we use a mixed-effects regression and include a magnitude-dependent finite-fault term and a site term, which are not included in the IPEs currently used for the Western US. The new IPE has much stronger saturation in magnitude scaling above M7 at shorter distances and a weaker magnitude dependence M5 at longer distances when compared to currently used IPEs for the western US (e.g., Atkinson et al. 2014). Although the intensity data is correlated to the peak velocity, the site term in the IPE is weak with a ln(VS30) coefficient of only -0.1 compared to -0.67 for peak velocity.

Session: Macroseismic Intensity: Past, Present and Future - I

Type: Oral

Room: Key Ballroom 12

Date: 4/17/2025

Presentation Time: 03:00 PM (local time)

Presenting Author: Ava Fathian Sabet

Student Presenter: Yes

Invited Presentation: Yes

Poster Number:

Additional Authors