Lithospheric Rheology in Southern California Derived From Novel Observations of Lake Unloading

Abstract

Recent Lake Cahuilla has undergone repeated filling and drying cycles over the past millennium, resulting in lithospheric and mantle loading responses. Two critical but less well‐constrained factors influencing these responses are the elastic plate thickness and mantle relaxation time. Using high‐resolution LiDAR surveys and GPS vertical velocity data, we refine estimates of present‐day shoreline elevations and invert for these geophysical parameters. The integration of LiDAR‐derived shoreline data provides a more detailed understanding of shoreline elevation and its variability than had been possible from previous studies. Long‐term vertical velocities from GPS stations help constrain the extent of any ongoing rebound associated with past water loads. Applying a viscoelastic rebound model, we estimate the plate thickness and mantle relaxation time that best explain the observed shoreline features. Our analysis reveals a model with an elastic thickness of 30 [±2] km and a mantle relaxation time of 25 [+10, −6] years that best represents vertical motions in the Earth's crust, offering new insights into the region's geodynamic processes. Our best fit model suggests that uplift in areas around the Salton Sea can potentially be as high as several centimeters over the course of several relaxation times (150 years) if the Salton Sea were drawn down completely.