Strong-motion Seismology, Site Response & Ground Motion

Predicted shaking intensity in the SF Bay Area for a Magnitude 6.9 earthquake on the southern Hayward fault.

Intense ground shaking during large earthquakes can damage or even cause failure of engineered structures such as buildings, bridges, highways, and dams. Sustained strong shaking can also trigger ground failures, such as rock falls, landslides, earth flows and liquefaction. Strong motion seismology uses special sensors, called accelerometers, to record these large-amplitude ground motions and the response of engineered structures to these motions.Recordings of large-amplitude seismic waves near the earthquake source can be used to investigate the fault motions that produced the earthquake.

Site response and ground motion studies use standard seismometers and oil-industry standard geophones to measure the local shaking from natural and man-made sources. These measurements help predict differential, site-dependent ground motion resulting from earthquakes.This information is used to upgrade building codes, to design earthquake-resistant structures, and to predict the patterns of strong shaking from future large earthquakes. Rapid reporting of shaking levels also helps to focus emergency response efforts in areas where damage is likely to be the greatest.

• Community Internet Intensity Maps (Did You Feel It?)
  Citizen science project that produces estimated intensity maps for United States earthquakes based on individuals' reports of shaking and damage. Did you feel it? Report your observations here.
  
• GEOS Home Page
  Reports and downloadable data from the USGS General Earthquake Observation System for nav-selected significant earthquakes since 1975, and for long- and short-term deployments.
  
• Ground Motion Studies
  Field response to damaging earthquakes, operation of dense seismic arrays and modeling of intense ground shaking are some of the responsibilities of this program.
  
• Memphis, TN Urban Hazard Mapping Project
  Download maps of earthquake ground shaking at a scale appropriate for urban planning and development, disaster mitigation and response planning. These account for local variations in soils and their effects on shaking. Raw data and posters also available.
  
• National Strong Motion Project (NSMP)
  This program has primary Federal responsibility for recording each damaging earthquake in the United States. It maintains a national cooperative instrumentation network, a national data center, and a data analyses and research center.
  
• Predicted Shaking for a Repeat of the Great 1906 Earthquake
  Automated slide show (15 minutes) reviewing the 1906 and 1989 earthquake damage, the application of GIS technology, and expected ground shaking maps for the San Francisco Bay Region.
  
• ShakeMaps
  Realtime maps of recorded ground motion in urban areas. Peak acceleration and velocity, and instrumentally-derived estimated Modified Mercalli Intensity.
  
• Site Response in the Pacific Northwest
  Shear velocity measurements in downtown Seattle are helping modelers predict damaging groundmotion from earthquakes.