Frequently Asked Questions
What magnitude scale does PlainQuake use?
PlainQuake uses the magnitudes as reported by USGS, which are primarily moment magnitude (Mw) for significant events. Mw is the modern standard based on seismic wave energy, replacing older scales like Richter (ML). The scale is logarithmic: M5 releases about 31.6× more energy than M4, and M6 releases about 1,000× more than M4.
Why are some countries listed with far more earthquakes than others?
Earthquake frequency correlates with tectonic activity, countries along plate boundaries (Japan, Indonesia, Chile, Mexico, the Philippines) experience far more earthquakes than geologically stable continental interiors. Indonesia and Japan consistently rank among the highest globally for M4+ earthquake counts because they sit at the intersection of major tectonic plates.
What is a 'significant earthquake' in PlainQuake?
PlainQuake defines significant earthquakes as those of magnitude 6.0 or greater from the USGS Significant Earthquake Catalog. M6.0 earthquakes are capable of causing serious structural damage near the epicenter, especially in densely populated areas with weak building stock. The USGS Significant Earthquake Catalog extends back to 1900 for this magnitude threshold.
Why are there fewer M4+ earthquakes listed for remote ocean areas?
Detection of M4-5 earthquakes requires nearby seismic sensors. Remote oceanic regions lack the sensor density of heavily instrumented areas like California, Japan, or Western Europe. An M5 earthquake in the middle of the Pacific Ocean may not appear in catalogs, while the same earthquake near a seismic network would be well-recorded. Coverage improves for M6+ earthquakes globally.
How often does PlainQuake update its data?
We update our earthquake database periodically from the USGS ComCat API. The current catalog covers events through 2025. For real-time earthquake information, use the USGS Earthquake Hazards Program directly at earthquake.usgs.gov.
What is earthquake depth and why does it matter?
Earthquake depth is the distance below the Earth's surface where the rupture originates. Shallow earthquakes (less than 70km) cause more surface shaking than deep earthquakes of the same magnitude because the energy travels a shorter path. Deep earthquakes (over 300km) occur in subducting slabs and are felt over wider areas at lower intensity.
Is PlainQuake affiliated with USGS?
No. PlainQuake is an independent data portal and is not affiliated with the US Geological Survey or any government agency. We use publicly available USGS ComCat API data to make global earthquake information more accessible.