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.

Regional Studies


  • Paleoseismology in the San Francisco Bay Area

    We are currently exhuming several faults in the San Francisco Bay region in search of their ancient earthquake (paleoseismic) histories. The process involves digging a trench across (or along side) the fault in order to map, date and interpret disturbances in the soil layers (geologic strata) seen in the facing walls of the trench.
  • Portfolio of Landscape, Seascape and Faults of the San Francisco Bay Area

    Developed by Robert E. Crippen (JPL) and Ross Stein (USGS), these images drape Landsat TM satellite imagery over Digital Elevation Models to show the bay as it has never been seen before.
  • Quaternary-Active Fault Map

    Shows the distribution of faults in the San Francisco Bay region most likely to generate future earthquakes, with information about active faults and how geologists find them and study them.
  • San Francisco Bay Region Geologic Map

    Shows the distribution of geologic materials and geologic structures that are visible at the Earth's surface, with information about geologic materials, geologic time, fossils, and the geologic history of the San Francisco Bay region.
  • The Parkfield, California Earthquake Experiment

    A comprehensive, long-term earthquake research project on the San Andreas fault to better understand the physics of earthquakes.

Intermountain West

  • Intermountain West Project

    Collecting and analyzing data that directly contribute to improving the National Seismic Hazard maps, and that better quantify the frequency and characteristics of earthquake-generated strong ground motion in seismically hazardous parts of the Intermountain West, particularly in the more heavily populated urban corridors of the region.

Pacific Northwest

  • Scientific Investigations in the Pacific Northwest

    USGS scientific investigations focus on improving our understanding of the causes and effects of Pacific Northwest earthquakes. In almost all cases a multi-disciplinary approach is required because near-surface evidence may be hidden by glacial deposits, extensive tree canopy, numerous water bodies.