Quantification of Unsteady Fault Slip and Fold Growth, Apennine Front, Italy

Lehigh University, Bethlehem PA

Investigators

Abstract

This research group proposes that blind thrust faults in the core of growing anticlines exhibit variable slip at 10,000 to 100,000 year time scales and that this slip is rooted in crustal-scale processes of stress transfer among faults responding to climatically-driven processes at the Earth?s surface. Studies along the mountain front of the northern Apennines, Italy will delineate the slip history of two related, but physically disconnected faults at a approximately 20,000 year resolution over a five million year Pliocene - Recent time span. Because this record of fault slip coincides with the well-known large amplitude oscillations in global climate that contribute to the filling and deformation of the Po foreland, the team further hypothesizes that the 100,000 year, and potentially 40,000 year climatic cycles will be reflected in observed slip rates as faults are differentially lubricated by changing ground water conditions, sea-level and structural emergence, and differentially loading by the redistribution of sediment at the surface. The project will employ cyclostraigraphy of anhysteretic remanent magnetization calibrated to accurate models of Earth's orbital motions, which constitutes a high-resolution metronome with a precision, accuracy and continuity that outperforms modern radioisotope geochronology, magnetostratigraphy, and biostratigraphy and transcends the problems of resolution and length of record that have limited GPS and paleoseismic approaches. Fault slip unsteadiness with a periodicity in line with known climatic cycles at 40,000-100,000 year time spans will prove the hypothesis. Knowledge of fault slip rate variation on a fault with 10,000-100,000 year resolution has important geodynamic, and seismic hazard implications particularly for the case of blind thrust faults that can generate significant earthquakes, such as the 2008 Los Angeles basin earthquakes. Similar kinds of earthquakes resulting from blind thrust faults are well documented for the northern Apennine (Italy) mountain front, home to 4 million residents where deformation rates and seismic hazards remain poorly defined. Here spatial and temporal gaps in earthquake activity are considered as places where damaging earthquakes do not or will not occur. This research suggests that such gaps are simply the result of fault slip unsteadiness and aims to determine a cause for the unsteadiness by studying the geologic record.