Seismic Monitor is a map made by IRIS which shows the data we have been given by other sources. IRIS’s current data sources are listed here.
Most apparent errors fall into two main categories: omission (where is a quake?) and mismatch (why is it different here then some other source?).
If it is an omission of a earthquake near you, please don’t take it personally. We likely have your earthquake recorded, but if it isn't above about 4 in magnitude it isn't included on this particular map. This is in order to have a globally-uniform distribution of earthquakes, which prevents certain regions appearing more seismically active merely because there are more seismic recording instruments.
A complete search for earthquakes at IRIS can be done here.
IRIS’ main focus is to store, analyze, and distribute seismic data, mainly digitized waveforms, from a variety of sources all over the world.
Our earthquake times, places and magnitudes may not perfectly match other data sources, such as websites or news reports.
Within the U.S. the earthquake authority is the USGS, and USGS maps and data feeds are excellent sources of information. Outside the U.S. you may find that your own regional authority is your best source.
Reasons we might differ from another website or news report include:
With so many sources of data, multiple reports of the same earthquake are common and can differ. IRIS does not edit or delete data that are reported, and selecting from differing reports for a earthquake is not an exact science.
Many people believe that an earthquake’s location, time and magnitude can be accurately determined immediately after it happens. In fact, the accuracy generally improves over the days and weeks after the earthquake.
Earthquakes are updated at various intervals at IRIS, such as immediately, hours later, daily, weekly and monthly. Preliminary details get refined as new measurements come in from more seismic stations and get analyzed.
People naturally check Seismic Monitor in the hours or days right after an earthquake, before the better measurements have come in.
There are also more than 8 different types of magnitude measurements seismologists use. One source may be reporting the moment magnitude and another the body wave magnitude, and they can differ. One source can also report multiple magnitude types for an event.
IRIS stores all these “versions” of an earthquake. We use simple rules to choose which version is our current “best” one. (To explore all the versions of our earthquakes there are more advanced tools, such as our SeismiQuery event search. )
Determining when a earthquake is a separate earthquake versus a differently-reported value for the same earthquake is not an exact science.
Occasionally two separately-listed earthquakes in Seismic Monitor may actually be the same one. Conversely, two different earthquakes may have been considered to be the same one.
Sometimes a data source agency may modify their website to reflect the very latest estimations and consensus values for an earthquake. These modifications may not be immediately included in the corresponding data sources which IRIS uses.