Paleoseismology

Paleoseismology reconstructs prehistoric earthquakes from geological evidence, especially faulted sediments and landforms. It extends earthquake histories beyond the short span of instrumental and written records.

Paleoseismic trenching: An excavation across a fault that exposes displaced layers and other evidence of past earthquakes. Trenches reveal successive ruptures as breaks and offsets in buried strata.
Active fault: A fault with evidence of recent geological movement and potential for future displacement. Paleoseismic investigations commonly target faults capable of recurring earthquakes.
Seismic hazard: The probability and expected severity of earthquake ground shaking or related effects at a location. Long-term rupture histories help characterize earthquake hazard beyond instrumental records.
Turkish–Syrian earthquake sequence: A sequence of major earthquakes that ruptured parts of the East Anatolian Fault system in February 2023. Its instrumentally recorded ruptures provide a modern comparison for trench-based fault histories.
Radiocarbon dating: A method for estimating the age of organic material from its content of radioactive carbon-14. Organic material above or below a rupture can constrain when the earthquake occurred.
Fault scarp: A step or steep slope at the ground surface formed by movement along a fault. Scarps can mark surface ruptures and guide trench placement.
Probabilistic seismic hazard analysis: A method for estimating the likelihood that specified levels of ground motion will be exceeded. Paleoseismic recurrence estimates can inform earthquake rates used in hazard models.
Cascadia megathrust: The subduction-zone fault offshore the Pacific Northwest, where the Juan de Fuca Plate descends beneath North America. Coastal subsidence and tsunami deposits document great prehistoric earthquakes along this fault.
Tephrochronology: Dating and correlating geological deposits using distinctive layers of volcanic ash. A dated ash layer can bracket an earthquake horizon in a trench.
Stratigraphy: The study and interpretation of layered rocks and sediments and their sequence through time. Reading layer order is essential to identifying and dating buried ruptures.

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