Lydia M. Staisch

Deformation history of the Doty fault system with implications for seismic hazard in western Washington​

​

The Willapa and Doty Hills, located in western Washington, were Miocene depocenters but now form uplifted topography. The Doty fault is a major structure that bounds the Doty Hills (Lincoln Creek uplift) in the west and south and is mapped as a series of north-dipping reverse faults. South of the Doty fault, a syncline deformed the mid Miocene Grande Ronde Basalt, suggesting post-Miocene deformation has occurred in this region. This project is a collaboration between the Washington Geological Survey and USGS to understand the timing and magnitude of deformation by mapping the fault zone and applying diverse geochronological and geophysical techniques.

 

The impetus for this project is that the frequency of flooding of the Chehalis River seems to have increased, with major negative impacts on local communities and major transportation corridors. A flood mitigation dam is one potential solution under consideration. Given its planned proximity to the Doty fault zone, the facility design required understanding of the magntiude and frequency of crustal earthquakes. The results from mapping, neotectonics, and seismic hazard will be used by engineering geologists to develop appropriate seismic parameters for use in the design of a flood-retention facility.