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Moment tensors and focal mechanisms of the October-November Denali Fault earthquake sequence - Abstract
On November 03, 2002, a magnitude 7.9 earthquake shook the interior of Alaska. This is the largest known event on the Denali Fault system. It was preceded by the M6.7 Nenana Mountain earthquake on October 23, 2002, which was located 44 km northeast of the Denali National Park entrance and 146 km south of Fairbanks. The Nenana Mountain earthquake ruptured 45 km of the Denali Fault. The Denali Fault earthquake initially occurred within the Nenana Mountain earthquake rupture zone, on the Susitna Glacier thrust fault. The earthquake propagated along the Susitna Glacier fault to the adjoining Denali strike-slip fault. The propagation continued eastward along the Denali fault until it reached the junction between the Denali and Totschunda faults, where the rupture transferred to the southeast trending Totschunda strike-slip fault. The rupture occurred over 345 km on three different faults with three distinct releases of concentrated energy in a time span of 1.5 to 2 minutes. Since the rupture propagated east, the majority of the energy released by the earthquake also propagated east, away from Fairbanks and Anchorage. This resulted in minimal damages in the two main population centers of Alaska. The most damage was in the town of Mentasta Lake, where on the nearby Tok Highway cutoff, the maximum fault offsets of 8.8 m were located.
The Alaska Earthquake Information Center (AEIC), the Alaska Volcano Observatory (AVO), and the Pacific Tsunami Warning Center (PTWC) cooperate the Alaska regional seismic network. The network consists of over 300 seismic stations. The stations have a variety of sensors: broadband, strong motion, and short-period. In addition to these permanent sites, an array of temporary stations, consisting of broadband and strong motion instruments, have been installed to record the aftershocks of the M6.7 Nenana Mountain earthquake and the M7.9 Denali Fault earthquake. Since the Nenana Mountain earthquake, more than 8000 aftershocks have occurred on the Denali Fault system.
We are analyzing the source parameters and rupture processes by determining moment tensors and focal mechanisms of these earthquakes and their aftershock sequences. Moment tensors and focal mechanisms allow us to understand how much energy was released and how the faults moved. The locations of the aftershocks are clarifying and defining surrounding fault structures. The moment tensors and focal mechanisms allow us to classify these structures. Other applications for moment tensors and focal mechanisms include refining the model of the velocity structure of Alaska and determining the states of stress of the Denali Fault system. By refining the velocity model of Alaska, we will be able to calculate more accurate earthquake locations. Knowing the states of stress will help us to better understand the behavior of strike-slip fault systems.
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