Comprehensive Seismic Hazard Assessment
Blueprint for an integrated and site specific approach of seismic hazard assessment.
Assessment of large scale tectonic features
Aim: presenting the geological and tectonic setting of the region and assessing the effect of large scale tectonic features on the project area.
Execution: interpreting and analyzing geological and tectonic maps, airphotos, deep seismic surveys and seismic catalogues as well as summarizing available information.
Assessment of local surface features
Aim: assessing the level of recent seismic activity and detecting surface ruptures or hazardous zones as well as identifying additional earthquake-triggered natural hazards (secondary effects).
Execution: surveying and mapping surface geology and geomorphologic features, interpreting airphotos and reviewing available literature, borehole logs and results of geotechnical testing.
Assessment of local subsurface features
Aim: assessing the quality and 3-D extent of the subsurface material for ground motion modeling as well as detecting, identifying and localizing hazardous subsurface features (inhomogeneities, blind subsurface rupture or fault zones, depth estimation of the water table).
Execution: Borehole drilling and material testing, 3-D imaging of subsurface features by correlating borehole logs (100 ft depth) with Ground Penetrating Radar (GPR) and/or Shallow Seismic Reflection (SSR) surveys.
Assessment of regional paleoseismicity
Aim: assessing the regional paeloseismicity (instrumental vs historical data) and evaluating seismogenic zone parameters (b-values, seismic migration and gaps, slip rates, spectrum, max magnitude).
Execution: documenting and dating ancient seismically induced failure features on buildings or lifelines as well as in nature (ruptures, fault zones, liquefaction, landslides, ground failures, subsidence) in the region, analysis of existing instrumental seismic data and literature.
Assessment of regional seismic parameters (off-site conditions)
Aim: determining and modeling earthquake source and path effects for the region.
Execution: locating the nearest active fault zone, determining and modeling fault zone parameters (geometry, size, shape, orientation, segmentation, max. magnitude recurrence rate) as well as designing attenuation curves specific to the region.
Assessment of ground motion (on-site conditions)
Aim: predicting the Peak Ground Acceleration (PGA) as a function of its dominating frequency for various part of the project area.
Execution: measuring in-situ ground motion, constructing response spectra from a series of time histories and modeling site specific PGAs as a function of dominant frequencies based on the analysis of both regional seismic parameters (source and path effects) and subsurface material parameters measured within the project area.
Assessment of additional earthquake triggered hazards (secondary effects)
Aim: detecting and assessing additional earthquake-triggered hazards (liquefaction, landslides, terrain instabilities and subsidence).
Execution: surveying and mapping surface geology and geomorphologic features and identifying suspicious subsurface structures on GPR and SSR profiles.
Comprehensive seismic hazard assessment
Aim: designing microzonation maps, evaluating site specific ground motion for engineering purposes, developing a catalogue of recommendations and devising mitigation strategies. The maps are based on public information and on a complementary set of geophysical measurements conducted by GeoSense.
Execution: designing isomaps for various levels of expected ground motion by correlating the 3-D extent of subsurface features with site specific response spectra, designing hazard maps with zones of potential earthquake-triggered liquefaction or landslide.
Final products
The comprehensive seismic hazard assessment of a specific area consists in a final project report which includes:
- Purpose of the study,
- The geological, tectonic and seismic setting,
- The available geological, seismic and geotechnical data,
- Results of new material testing (surface or subsurface)
- Results of subsurface investigations (boreholes, trenches, GPR, SSR),
- Site-specific response spectra,
- Seismic microzonation of the project area,
- Recommendations for a comprehensive mitigation of seismic hazard.
as well as a series of integrated GIS maps:
- Site map of the project area with location of all types of exploration (new and old),
- Geological map with bedrock, alluvium, colluvium, soil material, fault zones, springs and rock fall or landslide zones,
- Isomap for various levels of expected ground motion,
Hazard map with zones of potential earthquake-triggered liquefaction or landslides.
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