Weiwei Zhan

Weiwei Zhan

Assistant Professor at University of Central Florida

Parameter Sensitivity Analysis of the New Accelerogram-based Method

less than 1 minute read

The effectiveness of accelerogram-based liquefaction triggering procedure is relying on the two frequency-related parameters of surface ground motions (RL and MIFr). We selected eight factors to represent source, path, and site effects, and applied the one-way Analysis of Variance (ANOVA) method to rank the correlation between these eight factors and RL and MIFr separately. The results suggest that liquefaction generally has a dominant effect on RL and MIFr. However, earthquake magnitude and epicentral distance could have similar effects on RL or MIFr, respectively, as liquefaction does, which needs to be accounted for in applications and improvements of the accelerogram-based liquefaction triggering procedure.


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Open-source Geospatial Liquefaction Database and Associated Tools

OpenLIQ is a geospatial database of global seismic liquefaction hazards. The OpenLIQ database currently includes ~290,000 samples (~63% of them are liquefaction points) and 19 geospatial predictors for 51 worldwide earthquakes. In addition, the OpenLIQ project includes a semi-automatic GIS workflow that can automatically conduct geospatial sampling of liquefaction and non- liquefaction points from liquefaction inventories (georeferenced liquefaction points and/or polygons), extract candidate geospatial predictors, and generate maps for quality check and visualization purposes. This workflow only requires limited manual inputs (e.g., incomplete or complete liquefaction inventory, and raster data for geospatial predictors). The GIS workflow will be used to process new liquefaction inventories, and the OpenLIQ database will be used to advance applications of different machine learning and uncertainty quantification methods in global geospatial liquefaction modeling.

Evaluating the Accelerogram-based Liquefaction Detection Method Using Continuous Earthquake Recordings

I further evaluate the performance of the new method using continuous earthquake recordings at four seismic stations. The results suggest the method performs better at the soft-soil sites than at the stiff-soil sites and tends to make false negative predictions for very strong earthquakes. This study highlights the applicability of the new accelerogram-based method to regions with continuous earthquake monitoring.

Site Response Temporal Change Evaluation

To examine if the large interevent variability of seismic site responses at liquefiable sites is reducible, I investigated the temporal variability of seismic site responses at a liquefiable site using the sliding window spectral ratio method. I used stacked images of surface-to-borehole spectral ratios to track changes in seismic site response characteristics at temporal scales varying from seconds to decades. I observed that resonance frequencies dropped by ~70% during the mainshock of a liquefaction-triggering strong earthquake (indicating significant soil softening behaviors) and had an ephemeral increase by ~40% due to the strong soil dilatant behavior. In addition, I observed that the resonance frequency recovered after a strong earthquake at two phases with different recovery speeds and fluctuated along the seasonal changes of hydrologic conditions in the shallow subsurface.