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, magn...

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