The science of finding out the (pre-)historic earthquake history is called 'paleoseismology'. You can read about it from a variety of sources. In most instance

The science of finding out the (pre-)historic earthquake history is called 'paleoseismology'. You can read about it from a variety of sources. In most instances the earthquakes are dated by finding carbon-bearing material in deposits that look like they were created during the earthquake, and doing radiocarbon dating of them. The ages may be bracketed by radiocarbon dating of sediments that were clearly broken by the earthquake (and are therefore older) and ones that overlie the broken rocks (and are therefore younger). In a few other instances, earthquakes can be dated by tree-ring dating; for example during big subduction zone earthquakes, the coast often subsides by a meter or two, which will put some forested beaches under sea level (or at least high tide level) and kill all of the trees that can't deal with salt water. In others, the dates of sediment layers broken or caused by earthquakes can be dated through other means, or correlated with climate events of known time. Some example of deformed and undeformed sediments in the Wrightwood trench site on the San Andreas is here[0,1]. [2] is from the nearby San Jacinto fault. [3] has a lot of images. [4] is a good introduction to the science with good pictures. [0]: http://www.bssaonline.org/content/97/4/1054/F14.large.jpg http://www.bssaonline.org/content/97/4/1054/F14.large.jpg [1]: http://www.bssaonline.org/content/92/7/2726/F11.large.jpg http://www.bssaonline.org/content/92/7/2726/F11.large.jpg [2]: http://lithosphere.gsapubs.org/content/7/3/211/F6.large.jpg http://lithosphere.gsapubs.org/content/7/3/211/F6.large.jpg [3]: http://earthquake.usgs.gov/research/external/reports/04HQGR0083.pdf http://earthquake.usgs.gov/research/external/reports/04HQGR0... [4]: http://isites.harvard.edu/fs/docs/icb.topic988563.files/EPS203_paleoseis5r.pdf http://isites.harvard.edu/fs/docs/icb.topic988563.files/EPS2...