Love and Rayleigh waves
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
The Global Seismographic Network (GSN) is a 150+ station, globally distributed, state-of-the-art digital seismic network that provides free, realtime, open access data through the IRIS DMC. The map above shows the distribution of the current station network with respect to network operations.
The Global Seismographic Network is a cooperative partnership between IRIS and the U.S. Geological Survey (USGS), coordinated with the international community, to install and operate a global, multi-use scientific facility as a societal resource for Earth observations, monitoring, research, and education. The stations of the GSN attempt to obtain the best possible recording capability, balanced with global geographic coverage. GSN instrumentation measures and records with high fidelity all seismic vibrations possible from high-frequency, strong ground motions near an earthquake to the slowest global Earth oscillations excited by great earthquakes. Seismology has been the primary focus in the creation of the GSN, but the infrastructure is inherently multi-use and can be extended to other disciplines. Several GSN stations currently incorporate microbarographs, GPS, Geomag, and Meteorological packages.
Global Seismology. University of Michigan. (seismology, earth structure, earthquakes, imaging, tomography)