Felt Reports from the MyShake Smartphone App as an Earthquake Shaking Intensity Metric

Abstract MyShake is a free smartphone application that delivers earthquake early warning alerts to users in California, Washington, and Oregon. It also provides earthquake information and can gather community science earthquake data, such as earthquake shaking waveforms and felt report data, from users. In this study, we focus on the felt reports collected by the app: users can qualitatively report their experience of earthquake shaking on a simple five-point shaking scale. We leverage a MyShake felt report database of 314,999 records to evaluate the utility of MyShake felt reports for intensity mapping. We determine a linear relationship between the MyShake shaking scale and modified Mercalli intensity (MMI) values derived from the U.S. Geological Survey’s “Did You Feel It?” (DYFI) felt reports and show that the MyShake-reported shaking correlates well with MMI values from DYFI reports. We then demonstrate the performance of the MyShake shaking scale in shaking intensity maps for small-to-moderate earthquakes, highlighting the potential for MyShake felt reports to contribute to further intensity and ground-motion analyses. At higher intensity levels, damage corresponds to MMI better than felt shaking, and as such, our experience-based MyShake-to-MMI mapped values might present shortcomings at those levels.