Modeling and Interpretation of Ultraprecise Crustal Deformation Measurements

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

Modeling and Interpretation of Ultraprecise Crustal Deformation Measurements Duncan Carr Agnew This project is developing models to understand deformation signals observed over the last decade with precise strainmeters in southern California; these can measure very small changes in the ground over a range of periods from seconds to many months. The models and interpretive methods will be used elsewhere, for example to understand the signals to be be observed by the Plate Boundary Observatory (PBO) component of EarthScope. The data come from three sites in southern California: (1) Pinyon Flat Observatory (PFO) at which we operate three long-base strainmeters, two long-base tiltmeters, and many related sensors; (2) Durmid Hill (DHL), where we operate a single long-base strainmeter close to the San Andreas fault, and (3) Glendale, Los Angeles (GVS), where we completed a single long-base strainmeter in the fall of 2002. Some signals come from known sources, so that modeling them tests how adequate the usual simple models are for interpreting deformations from earthquakes and other tectonic changes. These signals include two types of surface loading near DHL (seiches and trains); for both of these the strains for an elastic halfspace directly contradict the observations. They also include the earth tides, which show significant distortions at both DHL and GVS, from laterally varying elastic structure and rugged topography respectively. We are also modelling less-understood signals, such as short-term strain changes seen at DHL, which we interpret as creep events on the San Andreas fault nearby, and changes related to the Landers and Hector Mine earthquakes.