Earthquake Geology & Paleoseismology
USGS and university geologists study the walls of a trench across a recently discovered strand of the Seattle fault.
Earthquake geology in the broad sense is the study of the history, effects, and mechanics of earthquakes within and on the Earth's crust. Most often, earthquake geology is synonymous with active tectonics, a term used to describe the study of tectonic movements that are expected to occur within a future time span of concern to society. Such definitions overlap considerably with other research topics on this site, such as Crustal Deformation, Seismology and Earth Structure, and Strong Motion and Site Response. Important aspects of earthquake geology include the study of tectonic landforms on the Earth's surface and folds and faults within its crust produced by many earthquakes over thousands to millions of years.
Paleoseismology is the study of the timing, location, and size of prehistoric earthquakes. Key to assessing the likelihood of such an earthquake is knowing how often they have occurred in the past, and when and how large the last one was. These questions underly the science of paleoseismology. Paleoseismologists, geologists who trench across faults, document evidence of paleoearthquakes, prehistoric earthquakes large enough to rupture the fault at the ground surface. By exhuming the top few meters of an active fault, paleoseismologists may find disturbed ancient soil layers or other traces left by past earthquakes. Exploratory trenches provide a valuable means to precisely locate and establish the recency of movement of particular fault traces. When dates of the past earthquakes can be estimated through the use of radiocarbon and other dating techniques, they provide a basis for estimating the probability of the next earthquake.