Types of data and methods

 

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There are several types of data and methods that are commonly used to determine the parameters of seismogenic sources. The list below is not intended to be exhaustive. Parameters in italics apply to Individual Seismogenic Sources only.

Location

  • Location of historical and/or instrumental earthquakes.
  • Geological maps.
  • Analysis of geologic, geomorphic, geodetic deformation.

Length (L)

  • Geological maps of faults expressed at the surface.
  • Geological cross sections across the active fault system.
  • Length of the area deformed by slip at depth identified as displaced or warped geological layers (folds) or geomorphic features (e.g. alluvial and coastal terraces), anomalous drainage pattern (e.g. allogenic stream/river migration/avulsion).
  • Scaling relationship between length and moment magnitude (e.g., LogL=a+b*Mw).

Width (W)

  • Geological sections across the active fault system.
  • Width of the area deformed by slip at depth identified as displaced or warped geological layers (folds) or geomorphic features (e.g. alluvial and coastal terraces), anomalous drainage pattern (e.g. allogenic stream/river migration/avulsion).
  • Combined analysis with the estimation of depth.
  • Scaling relationship between width and moment magnitude (e.g., LogW=a+b*Mw).

Depth

  • Depth distribution of instrumental earthquakes.
  • Geological sections across the active fault system.
  • Rheological profiles of the region.
  • Seismic tomography of the region.
  • Combined analysis with the estimation of width.

Strike, Dip, and Rake

  • Displacement components of geological markers in maps and cross sections.
  • Measurements of faults exposed at the surface.
  • Focal mechanisms of the larger associated earthquakes or other physical properties such as principal stress and strain axes.

Slip Rate (SR)

  • Displacement of dated geological markers.
  • Displacement observed through geodetic measurements.
  • Displacement calculated from seismic or geodetic strain.
  • Derivation from recurrence interval and slip (SR=D/RI).

Recurrence Interval (RI)

  • Time lag between successive event horizons identified in paleoseismological trenches.
  • Derivation from long-term slip rate (RI=D/SR).

Slip per Event (D)

  • Displaced geologic or geomorphic markers.
  • Analytical formulation of seismic moment based on the double-couple model (D=M0/μS, where μ is rigidity, S is fault area, and M0 is seismic moment).

Magnitude (Mw)

  • Largest magnitude of associated earthquake(s) measured instrumentally.
  • Largest magnitude of associated historical earthquake(s) estimated from intensity data.
  • Magnitude inferred from the area of the largest associated fault or fault set.
  • Magnitude inferred from a physical model that includes deformation data of any sort (e.g. geodetic, seismic, and geological).
  • Scaling relationship between magnitude and fault size (e.g. Mw=a+b*LogS, where S is fault size) or magnitude and single event displacement.


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