IRIS does not calculate earthquake locations and magnitudes but instead collects this data from multiple agencies in the U.S. and abroad.
This means you may sometimes see data that does not match those listed by another website or source.
A missing earthquake (in the case of Seismic Monitor, IEB, and other of our tools) is either due to it not being strong enough for inclusion in (Seismic Monitor has a minimum magnitude of about 4, to
achieve a globally-uniform distribution), or else the earthquake may not have been reported to us.
If the magnitude, time or location seems wrong, it is probably for one of these reasons:
- it is too soon after the earthquake, and the reports are preliminary (they get refined over days and weeks)
- a revision to a source's website has not yet been reflected in all their data feeds, as agencies sometimes update their public web pages before updating other products
- we get data from multiple sources, and reported values can differ
- there are various magnitude types for earthquakes, and we may be using a different type for this earthquake
- separate earthquakes, e.g. foreshocks, mainshocks and
aftershocks, have been considered to be the same single earthquake or vice versa (criteria for this vary amongst scientists)