Optimizing Magnitude Scaling Relationships in Simplified Liquefaction Triggering Procedures Using Ground Motion Intensity Measures

The magnitude scaling factor (MSF) accounts for the number of equivalent uniform loading cycles (Neq) in the simplified liquefaction triggering procedures from different magnitude earthquakes. Traditionally, MSF relationships have been developed based on earthquakes with magnitudes up to 8.0, primarily from shallow crustal sources. However, the effectiveness of these models for intra- and inter-plate subduction zone earthquakes has not been rigorously evaluated. This study critically examines existing magnitude versus number of uniform equivalent cycles (Mw–Neq) relationships for subduction zone earthquakes, utilizing data from the NGAWest2 and NGASub ground motion databases. It is shown that current Neq and resulting MSF relationships tend to overestimate the number of cycles for interplate subduction events in the moderate to high magnitude range, and intraplate earthquakes contain more loading cycles than current relationships predict. To address these discrepancies, an improved regression model for Neq that accounts for variability due to regional differences and earthquake source-type dependencies is introduced. This model integrates ground motion intensity measures of cumulative absolute velocity and peak ground velocity, each normalized by peak ground acceleration to enhance accuracy and offer a source-type agnostic framework for liquefaction triggering assessments. The proposed Neq model supports the development of the ground motion factor (GMF), which replaces the traditional MSF by extending beyond sole dependence on earthquake magnitude. The GMF, along with its associated Neq model, is designed to be compatible with the current triggering framework, and its adoption is recommended for complex earthquake source types.