USGS Earthquake Data & ShakeMap | Technical Information

USGS ComCat: the Earthquake Feed

Intensity Lab polls the USGS Comprehensive Catalog (ComCat) every 60 seconds for new and updated events. ComCat is the authoritative USGS earthquake catalog — it is where the magnitude, location, depth, and (when available) moment-tensor focal mechanism for every event used on this site originate.

A qualifying earthquake moves through the pipeline: detected → processing → published. If USGS has not yet published a ShakeMap for the event, it reverts to detected and is retried automatically.

Magnitude Floor & Geographic Coverage

Intensity Lab processes earthquakes of magnitude 3.5 and above. Below that threshold, ShakeMap coverage and public interest both drop off sharply, and the volume of near-instantaneous small events would swamp the notification and animation pipelines.

Supported region: latitude 28–50°N, longitude 125–113°W (Western US and northern Mexico), covering California, Nevada, Oregon, Washington, Idaho, and the Mexican states of Baja California and Sonora. Custom location queries outside this region are rejected by the API.

Data Source: USGS ShakeMap

All automated event reports are derived from USGS ShakeMap data. ShakeMap produces a spatial grid of estimated instrumental intensity (PGA, PGV, MMI) by interpolating from seismometer recordings and applying regional ground-motion models. Intensity Lab downloads the ShakeMap grid for each event and interpolates it at every gazetteer site — see Intensity Information & Examples for the interpolation method itself.

In addition to the interpolated grid, Intensity Lab also ingests the ShakeMap station list (stationlist.json) whenever USGS publishes one for an event — that file is what makes direct station observations possible; see Observed Seismic Station Data.

Station data availability: stationlist.json is typically present for M3.5+ events in California and other well-instrumented networks. For smaller events, events in sparsely instrumented regions, or events where ShakeMap was generated without a station list, the Stations view will indicate that no observed data are available. The Cities view (ShakeMap interpolated) remains the best available estimate in those cases.

From ShakeMap to Email Notifications

Registered users can opt into two types of automated email notifications, both driven directly by the ShakeMap-interpolated MMI computed above. All intensity estimates are computed and stored for every qualifying event regardless of notification delivery — data is always viewable on the website after logging in.

Site-Specific MMI Report

Sent to users who have registered a custom location when that site falls within the ShakeMap coverage area and the interpolated MMI there is ≥ IV (Light — generally felt indoors). Includes the ShakeMap-interpolated MMI, PGA, and PGV at the registered location, plus a comparison across four NGA-West2 GMPE models and nearby community shaking estimates.

Regional Event Summary

Sent to users subscribed to all regional events when the highest estimated MMI anywhere in the region is ≥ V (Moderate — felt by everyone, minor damage possible). Includes a map, nearby community MMI table, and a distance-intensity comparison plot.

Both notification types are evaluated independently — a user may receive both a site-specific report and a regional summary for the same event. Events below both thresholds are still fully processed; no email is generated, but all intensity data remains accessible on the website and via the API. Manage your notification preferences →