Examining the Influence of Fluvial Geomorphological Variables on Existing Empirical Models of Earthquake-Induced Liquefaction and Lateral Spreading

Abstract:

Earthquake-induced lateral spreading, which refers to permanent horizontal ground deformation from liquefaction, is a major geohazard that commonly occurs in river deposits. Improving models of lateral spreading is important for hazard forecasting, infrastructure development, and understanding how liquefaction affects the structure and preservation of fluvial deposits. Existing models include seismic loading (earthquake moment magnitude and distance from the source), topographic (slope), and basic stratigraphic parameters (fine content, the thickness of the liquefiable layer and median grain size), but do not account for depositional-environment-specific geologic conditions. This study uses case histories of lateral spreading in river deposits to determine which fluvial geomorphological variables should be incorporated into models of lateral spreading. We test a series of hypotheses to assess the impact of various features on the occurrence, extent, and severity of lateral spreading, and we developed appropriate proxy parameters to add to existing models for hypotheses testing and sensitivity analyses. Tested hypotheses include the following: 1) the actively deposited and younger sediments of a point bar are more susceptible to liquefaction than those outside of a meander bend, since younger sediments are generally less consolidated and have relatively low shear strength; 2) upstream regions of bars with better sorting and coarser grains will have increased susceptibility to liquefaction, as good sorting reduces the packing within the void spaces leading to relatively low shear strength; 3) fluvial deposits with higher dip angles, such as inclined heterolithic strata, will be more susceptible to liquefaction because of pre-existing static shear stresses. Based on case histories, including the New Zealand Canterbury earthquake sequence, we find that geomorphic conditions influence liquefaction triggering and lateral spreading. Results from this study help improve existing predictive models of lateral spreading and establish confidence intervals for the models based on the relevant fluvial geomorphic parameters. These results also suggest that the occurrence of lateral spreading could significantly impact the spatial continuity and preservation of ancient fluvial deposits.