Dr. Won-Young Kim
Earth Institute Contact: Dr. Won-Young Kim
Locations: United States of America
Northeastern United States
We will use local recordings of aftershocks of the Mw5.0 Au Sable earthquake, the best recorded aftershock sequence in the northeastern USA to characterize the source processes of earthquakes in stable continental regions (SCR). The collaboration between Abercrombie, an earthquake seismologist whose work focuses on source processes, and Kim, an earthquake seismologist who has considerable experience with Northeastern USA seismicity, including the Au Sable earthquake, is ideal for this study. Our research directly addresses the External Research Program Announcement for 2003, Element 1 and is applicable to the Research Priorities for FY2004 in the Central and Eastern United States region (CE).
On 20 April 2002, the Mw5.0 Au Sable Forks earthquake occurred in northern New York state. This earthquake is the largest to occur in the Northeastern USA since installation of the current broadband networks. A team led by Kim installed 12 portable stations which recorded 74 aftershocks (more than 10>M2) in 6 months. This is the first time that earthquakes throughout this magnitude range have been recorded on scale, by a local network, in the Northeastern USA. The aftershocks are also well recorded by the regional broadband networks. The ground motions recorded during this earthquake sequence provide a unique opportunity to study earthquakes source processes in the Northeastern USA. The low seismicity and relatively sparse seismic networks in stable continental regions mean that stress drop scaling for earthquakes in these regions is poorly known. This source information is an essential components of seismic hazard studies the scarcity of observations leads to large uncertainties in seismic hazard estimation. Our proposed study will determine whether small earthquakes in Northeastern USA obey the same scaling laws as earthquakes in active tectonic regions, or whether they have systematically higher stress drops like those observed for the small number of large earthquakes recorded in stable continental regions. We propose a one-year study of the Au Sable Forks earthquake aftershocks with three principal aims:
* Determine accurate source parameters. We will use both individual spectral techniques, and empirical Green’s functions to determine the source dimension, stress drop, and radiated energy of the M>2 aftershocks using both local and regional data.
* Validate previous regional wave studies in NE USA. Kim and colleagues have determined source parameters for 49 earthquakes in Northeastern USA using regional Sg and Lg waves. We will compare the results using local and regional waves for the Au Sable aftershocks and use the local measurements to validate and calibrate the regional wave measurements. We will then have a catalogue of over 50 earthquakes with well known source parameters.
* Investigate factors governing earthquake source process. We will compare the Au Sable aftershocks, and other NE USA earthquakes, to earthquakes in similar magnitude range in other tectonic settings to determine whether there are systematic differences in parameters such as stress drop or radiated energy. We will also compare them to larger magnitude earthquakes in stable continental regions.
The objective of this research is to characterize the source processes of small and moderate earthquakes in Northeastern USA. This will lead to both improved seismic hazard estimates, and a better understanding of the physics of the earthquake rupture process.
Cross Cutting Themes:
Hazards and Risk
US Geological Survey