Shaking intensity can be measured instrumentally, or determined from reports of earthquake effects. Shaking intensity varies from place to place, depending on earthquake size and distance, and geologic and topographic conditions. Before seismometers, intensities were measured by evaluating earthquake effects. The Modified Mercalli Intensity Scale was a standard scale. Currently, intensities are computed from a web-based form that allows people to record their impressions, and instrumental measurements of strong shaking are available to correlate with the human reports. More on Shaking Intensity from C. J. Ammon, St. Louis. U.

INTENSITIES FOR PACIFIC NORTHWEST EARTHQUAKES - Since the late 1990s, with some earlier info.

• ShakeMap - Instrumental Shaking from PNSN real-time instrumentation
• CIIM - Human Shaking Reports, collected on-line by the USGS in Pasadena CA

• Human Shaking Reports for older Pacific Northwest Earthquakes - Intensity reports are often combined into isoseismal maps - with countour lines delimiting geograhic areas of equal seismic intensity.
  • Duvall, 96/05/02 9:04 PM PDT
  • Bremerton 97/06/23 12:13:27.03 PM PDT
  • Satsop 99/07/02 06:43 PM PDT
  • NGDC Earthquake Intensity Database U.S. Intensity Data - 2,500 earthquakes reported from 1638-1928 and more than 18,500 events from 1928-1985.
  • 1929-1969 Earthquake information and Isoseismal Maps from United States Earthquakes, U.S. Department of Commerce, Coast and Geodetic Survey
  • Isoseismal Maps for the 1872 North Cascades earthquake: Various investigators have proposed different isoseismal maps for this large (M 6.8-7.4) crustal earthquake