Estimation of Radiated Seismic Energy from Teleseismic Body Waves

Ryota Kiuchi

        Earthquake radiated seismic energy is a fundamental parameter for understanding source physics. Using teleseismic waveforms, we can estimate the radiated seismic energy for a wide range of focal mechanisms and tectonic settings. We are especially interested in studying the apparent stress (rigidity multiplied by the ratio of radiated energy to seismic moment) of strike-slip earthquakes in the oceanic lithosphere, for which there are often high reported values (Choy and McGarr, 2002). Estimates of radiated seismic energy from teleseismic P waves can be unstable, because take-off angles from the source are often close to nodes in the focal mechanisms, which can cause large variations in the estimated values of the apparent stress.

        For strike-slip events with where many data are close to nodes in the focal mechanisms, this is a large and often unstable correction for the radiation pattern. In most studies, nodal arrivals are not used because of this problem. We use an improved method which takes into account uncertainties of values for the strike, dip and rake for nodal arrivals. This enables us to use more stations for the estimate of radiated energy. Also, we use station corrections determined from a selected set of well determined events.

        In this study, we use P waves for the teleseismic waveform, because of the interference with other phases for S waves. We use data recorded by teleseismic stations (epicentral distances of 30 to 90 deg) recorded on the GSN network and focal mechanisms published by USGS and Global CMT Project.

        Our energy estimate for 171 recent large earthquakes (>Mw 7.0, between 2000 and September, 2013) are studies for scaling with moment, depth dependence and focal mechanism differences. We see no strong dependence with seismic moment. Deeper earthquakes (>70 km depth) have slightly higher values of apparents stress compared to shallow events. We find that the strike-slip earthquakes have apparent stress values that are 5 to 6 times higher than dip-slip earthquakes with the oceanic events having almost same values with continental events. In addition, using our improved methods, we can estimate the apparent stresses for strike-slip earthquakes with more reliability, since the error of radiated seismic energies becomes smaller.