Remotely triggered earthquakes have now been observed commonly in geothermal and volcanic regions. Analysis of historic earthquake sequences reveals that remotely triggered earthquakes occur commonly in intraplate crust as well. Because neither abundant geothermal/volcanic fluids nor weak faults are expected to exist in intraplate crust, this provides evidence that at least some faults in intraplate regions are critically stressed.
Richter scale (ML), quantitative measure of an earthquake’s magnitude (size), devised in 1935 by American seismologists Charles F. Richter and Beno Gutenberg. The earthquake’s magnitude is determined using the logarithm of the amplitude (height) of the largest seismic wave calibrated to a scale by a seismograph.
When an earthquake happens deep underground a crack will start to open on a pre-existing line of weakness in the Earth's brittle crust. This crack will then grow larger and larger, relieving built-up stress as it goes.
When an earthquake happens deep underground a crack will start to open on a pre-existing line of weakness in the Earth's brittle crust. This crack will then grow larger and larger, relieving built-up stress as it goes.
Diagram of a seismic wave
Extremely Useful – But Not a Perfect System
Several well-known tomographic studies published in the 1990's (van der Hilst et al., 1991; Fukao et al., 1992) captured a large-scale subhorizontal high velocity anomaly at the bottom of the upper mantle in the northwestern Pacific. These models suggest that a large volume of subducted slab is stagnant in the transition zone.