In many parts of the world EARTHQUAKE HAZARDS pose a threat to public safety and a constraint on development projects. These hazards fall into 4 categories, each of which is mitigated differently:
SURFACE FAULT RUPTURE:
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During large earthquakes active faults rupture to the ground surface and displace it vertically and/or laterally. This hazard is difficult to mitigate, so it is generally avoided by: (a) locating the traces of the active fault, and (b) "setting-back" buildings from the fault trace. GEO-HAZ pioneered the empirical approach for determining fault setbacks in the 1980s. Click here to download PDF file "1987 Recomm Setbacks.pdf"
A little known fact is that even landfills are prohibited from crossing active (Holocene) faults, because surface rupture would compromise the barrier and collection systems (RCRA Subtitle D [258], Seismic Design Guidance for Municipal Solid Waste Landfill Facilities; EPA, 1995). The key issue is often dating whether the fault has moved in the Holocene, which requires expertise in fault geochronology/ paleoseismology.
Where avoidance is not possible, such as at pipeline fault crossings, paleoseismic studies can yield displacement parameters as a basis for an antiseismic fault crossing design.
PERMANENT ELEVATION CHANGES AND TSUNAMIS
Click for larger imageThe ground surface is permanently moved up or down and warped when active faults shift. Lake and ocean water may thus move toward (or in to) a site (or away from it), and gravity-fed pipes may change gradient. By calculating such effects in advance, mitigation can be included in design.
STRONG GROUND SHAKING (AMPLIFICATION]
Click for larger imageStrong ground shaking causes the most damage in earthquakes. GEO-HAZ maps the pattern and strength of shaking via Deterministic Seismic Hazard Analyses (DSHA; yields the largest,"worst-case" motions) or Probabilistic Seismic Hazard Analyses (PSHA; yields motions of a given probability of exceedance in a given time period).
GROUND FAILURE
Click for larger imageThe term ground failure is a general reference to landslides, liquefaction, lateral spreads, and any other consequence of shaking that affects the stability of the ground. GEO-HAZ uses GIS-based methods to analyze and map susceptibility and hazard for liquefaction and earthquake-induced landslides, including lateral spreads.
Earthquake Hazards