Deformation Models The rate of large events in fault-based ERFs depends directly on fault slip rates, which can be derived from measured and dated geologic offsets, and perhaps interpolated or extrapolated along faults. Slip rates can also be obtained by modeling geodetic measurements such as Global Positioning System (GPS) observations. Because it is impossible to identify all faults, another contribution to hazard can be deformation (in quotes here because this “off-fault” deformation is at least partially occurring on un-modeled faults), which can be inferred from observed seismicity and/or GPS observations. Only about thirty percent of UCERF2 faults had measured slip rate estimates, and most others had an estimate from only a single location. UCERF2 deformation models were therefore based on expert-opinion evaluation of geologic and geodetic data. In addition to on-fault slip rates, off-fault deformation was represented by a set of geographic polygons, referred to as “type C zones”, each of which was assigned an effective slip rate (Figure 5, top panel). As an a check, UCERF2 deformation models were summed across various transects to confirm posteriori that total plate tectonic rates were well matched. For UCERF3, we have developed four different deformation models. One is a geologically model (uninfluenced by GPS observations), while the other three are “pure” kinematically consistent models that directly include both geologic and geodetic constraints. By using these models, we minimize relying on expert opinion to broker discrepancies between geodetic and geologic data, as in UCERF2. Importantly, this approach has provided data-driven slip rate estimates for faults with no prior assigned rates (which were excluded from UCERF2) and has filled in slip rates along faults with sparse observations. The latter three models also provide off-fault strain rate maps, allowing us to abandon the UCERF2 type C zones.
Deformation Models The rate of large events in fault-based ERFs depends directly on fault slip rates, which can be derived from measured and dated geologic offsets, and perhaps interpolated or extrapolated along faults. Slip rates can also be obtained by modeling geodetic measurements such as Global Positioning System (GPS) observations. Because it is impossible to identify all faults, another contribution to hazard can be “off-fault” deformation (in quotes here because this deformation is at least partially occurring on un-modeled faults), which can be inferred from observed seismicity and/or GPS observations. Only about thirty percent of UCERF2 faults had measured slip rate estimates, and most others had an estimate from only a single location. UCERF2 deformation models were therefore based on expert-opinion evaluation of geologic and geodetic data. In addition to on-fault slip rates, off-fault deformation was represented by a set of geographic polygons, referred to as “type C zones”, each of which was assigned an effective slip rate (Figure 5, top panel). As an a posteriori check, UCERF2 deformation models were summed across various transects to confirm that total plate tectonic rates were well matched. For UCERF3, we have developed four different deformation models. One is a geologically “pure” model (uninfluenced by GPS observations), while the other three are kinematically consistent models that directly include both geologic and geodetic constraints. By using these models, we minimize relying on expert opinion to broker discrepancies between geodetic and geologic data, as in UCERF2. Importantly, this approach has provided data-driven slip rate estimates for faults with no prior assigned rates (which were excluded from UCERF2) and has filled in slip rates along faults with sparse observations. The latter three models also provide off-fault strain rate maps, allowing us to abandon the UCERF2 type C zones.
UCERF3pt3_Report_v13.tmpt1.docx