Earthquakes
Large earthquakes in Central and Eastern North America share some similar characteristics (in terms of what controls them — we’ll refer to them here in the form of a plural noun: controls); further, those characteristics and controls differ from earthquakes in Western North America.
What do I mean, in general, by controls on earthquakes? (Note, this exact term is not in the text; you will need to understand the various mechanisms in these two regions in order to answer this question sufficiently.)
How do those common characteristics and controls in Central and Eastern North America differ from Western North America?
Identify and discuss one characteristic and control that is unique to each region (Central/Eastern North America and Western North America; there are specific characteristics here, read and answer carefully.)
Earthquakes
By controls on earthquake, it means the measures that can be used to foresee and predict the size, distribution, and impact of an earthquake. The eastern North America region is made is composed of older rocks that were formed earlier that the rocks of the west. The Eastern North America region rocks have been exposed to extreme temperatures and pressures which makes them denser and harder. Seismic waves travel faster through the faults that occur on these rocks. The rocks in the West are much younger and when broken up by fault doesn’t heal on time, therefore, more of the seismic wave energy is absorbed by the faults and the seismic wave does not travel effectively. There are more earthquakes in the Western America region as it lies along the boundaries of the major tectonic plates; the ocean plates to the west and the North American plate. These plates are in motion and result in the breaking up of the crust along many faults. In the east, the faults are less active as they lie entirely within the North American Plate.
Earthquakes in Eastern North America have close and uniform repeat times. Western North America has a wide range that shows the tendency to increase with earthquake repeat time accordingly. There is a great variability to the source characteristics of the western earthquakes and there is the tendency that the effects decrease with slightly seismic activity.
For the North American plate, its earthquakes are common of earthquakes at Convergent boundaries. Its background seismicity at this convergent boundary is predominantly near the upper side of the subducting plate. The frequency of the earthquakes is greatest near the surface and around where the subduction happens and extends to at least a depth of 400km. It extends a few hundred kilometers away from the plate boundary.
References
Ghosh, A., Holt, W. E., & Bahadori, A. (2019). Role of Large‐Scale Tectonic Forces in Intraplate Earthquakes of Central and Eastern North America. Geochemistry, Geophysics, Geosystems, 20(4), 2134-2156.
Parker, G. A., Stewart, J. P., Hashash, Y. M., Rathje, E. M., Campbell, K. W., & Silva, W. J. (2019). Empirical linear seismic site amplification in Central and Eastern North America. Earthquake Spectra, 35(2), 849-881.
