How many earthquakes happen, and what about Los Angeles?

Steps

1. ComCat FDSN event service: query?format=csv&starttime=2025-10-01T00:00:00&endtime=2026-10-01T00:00:00&minmagnitude=4.5&eventtype=earthquake&orderby=time-asc (world, magnitude 4.5 or more, 7720 events, equal to the count service); count?minmagnitude=M for M 4.5 to 8.0 by 0.1 over Oct 2016 to Sep 2026; California: a box 31.5 to 42.5 N and 125.5 to 114 W, magnitude 3 or more, each 12-month period Oct to Sep, events whose place text names Nevada, Mexico, Oregon, Baja or Arizona removed; Los Angeles: latitude=34.05&longitude=-118.25&maxradiuskm=100&minmagnitude=3 (an API circle, checked against the count service); historic: maxradiuskm=100 with magnitude 5.8 or more and maxradiuskm=300 with magnitude 6.8 or more, all years, aftershocks within 3 days of a larger quake removed.
2. Counts are of events in ComCat with eventtype earthquake. Magnitude is ComCat's preferred magnitude (mostly moment magnitude for large events, body-wave magnitude for many small ones). The world catalogue is treated as complete from magnitude 4.5 (the count per 0.1 bin falls steadily from 4.5, tested by the script). Depth classes are the USGS ones: shallow 0 to 70 km, intermediate 70 to 300 km, deep 300 to 700 km. Region is the text after the last comma of the USGS place, with compass words and the word region removed.
3. Gutenberg-Richter: the cumulative counts come from the ComCat count service for each magnitude from 4.5 to 8.0 in steps of 0.1; the b-value is the Aki (1965) maximum-likelihood estimate. The USGS probabilities are copied from the fact sheet and parsed from its PDF text; nothing is recomputed.

7,720 world events, 10 yearly periods for California and Los Angeles, 19 historic events, 8 magnitude thresholds. Unit: events (earthquakes of the stated magnitude or more), magnitude as ComCat's preferred magnitude rounded to 0.1, depth in km, probabilities in percent as quoted. Every derived figure on this page (changes, indexes, averages, counts) is computed from the published rows, and the table under each chart says how.

Checks

• The world CSV has 7,720 rows, equal to the ComCat count service for the same window; event ids are unique; every event falls inside the window and has a magnitude of 4.5 or more and a depth between -5 and 800 km.
• Monthly counts, depth classes, regions and ten-year magnitude bins each add up to the total.
• The catalogue is checked for completeness from magnitude 4.5: the number of events per 0.1 step falls steadily from 4.5 (1937, 1490, 873, 651 for 4.5 to 4.8).
• The 20 events of the USGS list of largest earthquakes were each matched to one ComCat event by date, time and place; magnitudes differ by at most 0.
• The Los Angeles ten-year count from the service (198) equals the sum of the ten yearly queries (198); the Ridgecrest earthquake of magnitude 7.1 appears in the California events; well-known events (Northridge, San Fernando, Long Beach, Whittier Narrows) must be in the ComCat list or the script stops.
• The USGS definitions of depth classes, the long-term average (16 major earthquakes a year) and the copyright wording are read from the USGS pages and checked by the script. The 30-day globe layer (1,833 events, 127 KB) is rebuilt with one command.

Caveats

• ComCat is a mixed catalogue: magnitudes come from several agencies and methods, so counts near the magnitude 4.5 edge move when USGS revises an event. Region names are the USGS place text, not a tectonic map: Indonesia and the Philippines are national names, and ocean ridges appear under their own names. The ten-year California counts carry no completeness test and depend on the regional networks. Historic entries before 1900 are estimates from accounts, not instruments. Aftershocks are part of the counts: one large quake can add hundreds of events.
• The numbers describe recorded earthquakes, not damage or casualties, and a count of past events says nothing about when or where the next large one will be.
• A forecast probability such as the USGS 30-year figure is a long-term average over a region and a period. It is not a prediction of a date.

Releases and revisions

• The catalogue changes daily as USGS reviews events; this build is the Oct 8, 2026 snapshot. Re-run space_earthquakes.py to refresh (about 60 requests), or with --layer to refresh only the 30-day globe layer.
• USGS revises magnitudes and locations as events are reviewed; the layer of the past 30 days uses automatic solutions for the newest hours. The USGS fact sheet is dated 2015; check the USGS site for a newer forecast before quoting these probabilities elsewhere.