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Wide-aperture beamforming of depth phases by timescale contraction

Verification Program Geological Survey of Canada, 7 Observatory Cres., Ottawa, Ontario, Canada , K1A 0Y3

Abstract

Teleseismic depth phase signals can be combined with constructive interference from stations spaced as much as 1000 km apart. Each trace is first deconvolved using an operator based on the P phase of that trace, then its timescale is stretched or contracted to eliminate the moveout of pP-P time with distance. Traces can then be added with constructive interference of depth phases out to 10° or more angular distance between the stations on the focal sphere.

Depth phases (pP or sP) representing hypocentral depths ranging from 6 to 204 km were found using Canadian National Seismograph Network (CNSN) data for 45 events, recorded at ranges of 2000 to 10,800 km, which had been reported in the Reviewed Event Bulletins (REB) of the Prototype International Data Center (PIDC), including 23 events for which the REB reported no depth phases. For 28 events for which a catalog depth (REB; or PDE from USGS) was available for comparison, 18 had depths agreeing either within 6 km or within 15%, 7 can be explained by assuming an sP phase was misassociated as pP, 1 is just outside the error bar of the free depth reported in the REB, and only 2 disagree significantly.

Thus, using only Canadian data, depth phases were found by beamforming for many events for which no depth phases had been found by the PIDC using worldwide data including arrays. The depth phase beamforming method has the potential of substantially increasing the number of earthquakes for which teleseismic depth phases can be detected.

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