Tectonic Geomorphology and Near-Field Geodesy

Science Center Objects

Repeated earthquakes shape the Earth over the millennia and fault zones often have unique and diagnostic landforms caused by the faulting process.

In order to measure the rate at which the Earth’s crust deforms between, during and after earthquakes, precise measurements need to be made along active faults zones.

Overview  |  Earthquake Geology and Paleoseismology  |  Tectonic Geomorphology and Near-Field Geodesy

Earthquake Response  |  Salton Seismic Imaging  |  Special Earthquakes, Earthquake Sequences, and Fault Zones

 

Tectonic Geomorphology

USGS student interns using a terrestrial laser scanner and GPS

USGS student interns using a terrestrial laser scanner and GPS to map the elevation and deformation patterns of marine terraces along the northern California coast. Marine terraces are flat areas cut by the wave energy during times of high sea level. In area in which mountains are growing, the elevation and ages of adjacent flights of marine terraces can reveal the pace at which mountain growth occurs.(Public domain.)

Repeated earthquakes shape the Earth over the millennia and fault zones often have unique and diagnostic landforms caused by the faulting process. These include steep scarps, folds, elongate ridges, sag ponds, offset terraces, and linear valleys, and deflected, offset and uplifted streams. By studying these landforms, USGS geologists uncover the location and pace at which faults deform the Earth’s surface. Determining the rate at which a faults “slips” is a key piece of information for assessing the hazard that a fault presents to people and infrastructure. Scientists use airborne laser mapping elevation data to create remarkable visualizations of the shape of the Earth’s surface, even in areas covered by vegetation.

The study of landscapes affected by tectonics, often referred to as “tectonic geomorphology,” also provides important clues about seismic hazard associated with areas beyond the well-defined fault traces. The mountain ranges along the California coast are testament to the combination of sliding and squeezing that occurs at the boundary between the Pacific and North American tectonic plates. Mountains grow as a result of many earthquakes that occur over time as one side of a fault moves up relative to the adjacent side, or a large area is bent and warped upward. Some earthquakes, such as the 1989 Loma Prieta earthquake in the Santa Cruz Mountains south of San Francisco, are associated with the growth of mountains. These types of hazards are better understood by studying uplifting landforms such as marine terraces and other sedimentary deposits and by analyzing the patterns of river channel topographic profiles.

Near-Field Geodesy

3D laser scanner lofted by a helium balloon

USGS scientists and collaborators surveying the San Andreas Fault using a 3D laser scanner lofted by a helium balloon. (Public domain.)

The USGS is at the cutting edge of measuring ongoing deformation of the Earth’s surface, a field known as geodesy. In order to measure the rate at which the Earth’s crust deforms between, during and after earthquakes, precise measurements need to be made along active faults zones. USGS scientists have long established alignment arrays, which are stable markers that cross faults zones and can be measured to determine the rate of slip on the fault zone. USGS scientists, along with collaborators from universities, have established a network of hundreds of alignment arrays across the major faults of northern California.

USGS scientists are also at the leading edge of utilizing 3D laser scanning to map the Earth’s surface and objects at and near the Earth’s surface in order to quantify the rates and patterns of crustal deformation. This includes using 3D laser scanning technology from tripod mounts as well as mobile platforms (vehicles, backpacks, balloons, etc) that enable measurement of landscapes at centimeter-level precision over large areas. These techniques allow USGS scientists to provide rapid scientific response to damaging earthquakes, and to advance our understanding of the physics of earthquakes and how earthquakes affect the Earth in three-dimensions and through time.