Earthquakes in the past 7 days of magnitude 4.0 or greater
An earthquake swarm is a sequence of seismic events occurring in a local area within a relatively short period of time. The length of time used to define the swarm itself varies, but may be of the order of days, months, or even years. Such an energy release is different from what happens commonly when a major earthquake (mainshock) is followed by a series of aftershocks: in earthquake swarms, no single earthquake in the sequence is obviously the mainshock. In particular, a cluster of aftershocks occurring after a mainshock is not a swarm
Arkansas swarm
The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is also known as a fault-plane solution. Focal mechanisms are derived from a solution of the moment tensor for the earthquake, which itself is estimated by an analysis of observed seismic waveforms. The focal mechanism can be derived from observing the pattern of "first motions", that is, whether the first arriving P waves break up or down. This method was used before waveforms were recorded and analysed digitally and this method is still used for earthquakes too small for easy moment tensor solution. Focal mechanisms are now mainly derived using semi-automatic analysis of the recorded waveforms
Focal mechanism and method for controlling focal point position, and apparatus and method for inspecting semiconductor wafer - Patent 6541747
This page explains the concept of focal mechanisms.
A foreshock is an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space. The designation of an earthquake as foreshock, mainshock or aftershock is only possible after the full sequence of events has happened
General Earthquake Models (GEM)
A Program to Enhance Understanding of Earthquake Physics through High Performance Computation
Seismogram Viewer
The Global Seismogram Viewer automatically creates clear plots of seismograms of large earthquakes from stations around the world, displayed by distance from the earthquake. The plots are tablet-friendly and can also be printed for use in a classroom without computers. The plots are designed to be appropriate for use with no parameters to set, but users can also modify the plots, such as including a recording station near a chosen location. A guided exercise is provided in the related resources tab (above), where students use the seismograms to discover the diameter of Earth’s outer core. Students can pick and compare phase arrival times onscreen which is key to performing the exercise. A companion station map shows station locations and further information and is linked to the seismogram plots.
Key points:
Discover how Earth’s core was found and first measured
Select a large recent or newsworthy earthquake, and optionally include a nearby recording station
The resulting interactive plot allows students, via a classroom activity, to discover the P-wave Shadow Zone and how it can be used to determine the diameter of Earth’s outer core