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.
Quantification of Unsteady Fault Slip and Fold Growth, Apennine Front, Italy EAR 0809722 Anastasio, D. J., Kodama, K. P., Pazzaglia, F. J. Earth and Environmental Sciences Lehigh University and Smith, D. L. Da Vinci Science Center Earthquakes, some of which can be large, deadly, and costly, are a constant reminder that we live on a dynamic planet where tectonic forces deform the crust and build mountains. In an effort to better understand mountain building, earthquakes, and the processes that cause them, geologists rely on the history of earthquakes assembled from instrumented and human records. Much has been learned using this approach and we now have a clear picture of plate boundaries where large, damaging earthquakes are frequent. But even at plate boundaries, these records indicate that earthquakes are commonly unsteady in time and non-uniform in location. The lack of a clear historic pattern in earthquake behavior makes them particularly difficult to predict, which in turn severely limits our ability to mitigate the cost of earthquake hazards measured in human lives, damage to property, and economic loss. The problem lies in the short length of the instrumented and historic records that at best may cover 100 and 2000 years, respectively. In this research we identify a geologic setting where crustal deformation accommodated on actively-slipping faults and growing folds by earthquakes has been occurring for millions of years that allow us to discern the long-term patterns of when and where they occur. Using established geologic techniques such as biostratigraphy and magnetostratigraphy combined with novel methods such as cyclostratigraphy, we have investigated a section of deformed rocks and sediment in northern Italy along a plate boundary where the rugged topography of the Apennine Mountains meet the flat lands of the Po Plain. We chose this location for our study because the rocks are particularly well-exposed, linked to mapped faults that we know are responsible for their deformation, and generate earthquakes in this tectonically active region. Furthermore, Italy in one of those few places where a long, reliable historical record of earthquakes has been assembled. We are able to demonstrate that the uplift and deformation of the Apennine mountain front by repeated earthquakes (Figure 1) has indeed been variable in space and time not only over human time scales, but also over geologic time scales measured in millions of years. Looking at the data over these long time scales, we are able to discern a pattern. For example, near Parma, Italy, a period of earthquakes clustered in space and time built the Apennine mountain front approximately 1.4 million years ago. The number of earthquakes diminished considerably in the subsequent million years, but has increased again in the past 100,000 years, indicating perhaps that the mountain front is entering a new phase of rapid growth. The impacts of our research are significant in that they help geoscientists bridge the temporal and spatial gap between instrumented, historical, and geologic records of earthquakes. It also demonstrates how established and novel methods for documenting time and space patterns in earthquakes over long periods of time can be ported to other places away from plate boundaries, including many parts of the United States, where earthquakes pose a natural hazard of unknown severity. In addition to our insights into the deformation and earthquake history of the Apennine mountain front, this project compiled extremely detailed and complete lithostratigraphic, biostratigraphic, magnetostratigraphic, and cyclostratigraphic data sets from several sequences of rocks deposited during deformation (e.g. Figure 1). These sequences capture evidence of a number of important behaviors of the Earth, in addition to deformation, including changes in climate and evolutionary changes in living organisms. These data have been used to construct laboratory activities suitable for middle school or high school earth science classes and activities suitable for undergraduate or graduate stratigraphy courses. These educational activities use research-based pedagogical strategies to engage learners with these real world data sets. Real-world problem solving increases student motivation and engagement and these activities could help engage and train the next generation of geoscientists. As an example of putting this learning into practice, the laboratory exercises have been used as part of high school science teacher workshops of the Greater Allentown Math and Science Partnership sponsored by the Da Vinci Science Center, Allentown, PA.
