Identification of Deep Earthquakes
LOS ALAMOS NATIONAL LAB NM
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The objective of this project is to identify and apply seismic event discriminants that will reliably separate small crustal earthquakes magnitudes less than about 4 and depths less than about 40 to 50 km from small, deep earthquakes depths between about 50 and 300 km. These deep earthquakes are known to occur in the Asia-India continental collision zone, mostly north of the Indian subcontinent, including far western China. Not only are the depths of these subcrustal earthquakes difficult to reliably estimate using conventional arrival time location methods when event-station distances are large, but they can also appear with explosion-like characteristics on discrimination plots designed to separate nuclear explosions from crustal earthquakes. Thus, reliably flagging these small, deep events is critical in improving discrimination performance, because deep earthquakes can immediately be removed from further event identification analyses. Further, reliably identifying subcrustal earthquakes will allow us to eliminate deep events previously misidentified as crustal earthquakes from research datasets, thereby refining event identification parameters for the Magnitude and Distance Amplitude Correction MDAC process and ultimately leading to more robust capabilities for separating small, crustal earthquakes from explosions. Our research approach involves 4 primary steps 1 assemble a control data set of waveforms from reliably located, mostly larger earthquakes both crustal and deep events from the Hindu Kush region, 2 measure body-wave and coda-wave amplitudes of the control earthquakes, 3 experiment with amplitude ratios and other measurements as discriminants for separating crustal and deep events, and 4 apply the discriminants to a data set of small Hindu Kush earthquakes and assess discrimination performance.