Earthquake Geology and Paleoseismology Overview
The goals of USGS earthquake geology and paleoseismology research are 1) to make primary observations and develop ideas to improve our understanding of the geologic expression of active faulting, and 2) to acquire data that will improve the National Seismic Hazard Model. Geological research allows us to characterize faults, including the identification of secondary seismogenic structures, to study how fault zones evolve, and to characterize how tectonics are recorded in the geologic record and on the landscape.
Although the principal faults of the San Andreas Fault system and Pacific-North American plate boundary pose significant hazard to people, infrastructure, and the economy, the earthquakes that have affected the United States recently have occurred on a wide variety of smaller faults in the Western US with a range of kinematic behavior. Understanding a fault’s slip behavior, as well as its length and connectivity with other nearby faults, is important for constraining the magnitude range and frequency of earthquakes that a particular fault is likely to produce.
We use a mix of techniques from paleoseismology (excavating trenches), describing and dating sedimentary layers affected by earthquakes, mapping and dating landforms offset by earthquakes, and measuring past and current motion of active faults using alignment arrays, global positioning systems (GPS), and airborne, terrestrial and mobile laser scanning technology. Much of the work is field-based and special attention is paid to urban areas.
By excavating trenches across active faults, USGS geologists and collaborators are unraveling the history of earthquakes on specific faults. Damaging earthquakes often rupture along a fault up to the ground surface, and, in doing so, offset layered sediments that were deposited by water, wind and down-slope movement. Following an earthquake, new sediment may be deposited across the disturbed land, creating a new undisturbed horizon that is younger than the earthquake.
Geologists use radiocarbon dating and other methods to learn the age of pre-existing layers affected by ancient earthquakes as well as the new layers deposited after the earthquakes, and, by doing so, constrain a fault’s earthquake history. These methods work best at sites on faults that lie near streams, slopes, ponds and other areas that have frequent sediment deposition.
GPS and alignment arrays monitor slow crustal movements, and scanning techniques reveal data that would otherwise be unobservable to the human eye.
Scientists have successfully pieced together the history of earthquakes over the past several hundred to a few thousand years on many active faults. These histories provide insight into the possibility of future damaging earthquakes.
The goals of USGS earthquake geology and paleoseismology research are 1) to make primary observations and develop ideas to improve our understanding of the geologic expression of active faulting, and 2) to acquire data that will improve the National Seismic Hazard Model. Geological research allows us to characterize faults, including the identification of secondary seismogenic structures, to study how fault zones evolve, and to characterize how tectonics are recorded in the geologic record and on the landscape.
Although the principal faults of the San Andreas Fault system and Pacific-North American plate boundary pose significant hazard to people, infrastructure, and the economy, the earthquakes that have affected the United States recently have occurred on a wide variety of smaller faults in the Western US with a range of kinematic behavior. Understanding a fault’s slip behavior, as well as its length and connectivity with other nearby faults, is important for constraining the magnitude range and frequency of earthquakes that a particular fault is likely to produce.
We use a mix of techniques from paleoseismology (excavating trenches), describing and dating sedimentary layers affected by earthquakes, mapping and dating landforms offset by earthquakes, and measuring past and current motion of active faults using alignment arrays, global positioning systems (GPS), and airborne, terrestrial and mobile laser scanning technology. Much of the work is field-based and special attention is paid to urban areas.
By excavating trenches across active faults, USGS geologists and collaborators are unraveling the history of earthquakes on specific faults. Damaging earthquakes often rupture along a fault up to the ground surface, and, in doing so, offset layered sediments that were deposited by water, wind and down-slope movement. Following an earthquake, new sediment may be deposited across the disturbed land, creating a new undisturbed horizon that is younger than the earthquake.
Geologists use radiocarbon dating and other methods to learn the age of pre-existing layers affected by ancient earthquakes as well as the new layers deposited after the earthquakes, and, by doing so, constrain a fault’s earthquake history. These methods work best at sites on faults that lie near streams, slopes, ponds and other areas that have frequent sediment deposition.
GPS and alignment arrays monitor slow crustal movements, and scanning techniques reveal data that would otherwise be unobservable to the human eye.
Scientists have successfully pieced together the history of earthquakes over the past several hundred to a few thousand years on many active faults. These histories provide insight into the possibility of future damaging earthquakes.