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Towards the Automatic Relocation of Intermediate-Depth Earthquakes Using Adaptive Teleseismic Arrays

Description: 

The accurate location of intermediate-depth earthquakes has proven to be one of the more enduring problems in global seismic location studies. Complicated in many cases by a paucity of near-field observational data, the determination of accurate source depths for such earthquakes, in particular, has proven to be elusive. As a result, and despite improvements in recorded seismic data density and quality, the distribution and controls of these events remain poorly understood.

Depth phases (near-source surface reflections, e.g. pP and sP) are crucial for the accurate determination of earthquake source depth using global seismic data. However, such phases are often difficult to detect, suffering from low signal-to-noise ratios, and are disguised in the P-wave coda, and often suffer from an ambiguity as to which depth phase has been observed.

To address this limitation, we develop an automated approach to group globally-distributed stations at teleseismic distances into ad-hoc arrays with apertures of 2.5 degrees, before optimising and applying phase-weighted beamforming techniques to each array. We then use the resulting vespagrams from each medium-aperture array to automatically pick phase arrivals for the direct and depth phases, and determine differential arrival times between the depth phases and their corresponding direct arrival. These are subsequently used to invert for a new hypocentre location. We demonstrate this method by relocating all intermediate-depth events above a magnitude 4.7 associated with a region of northern Chile and the Peruvian flat slab region of the subducting Nazca plate. We demonstrate that our approach leads to a radical increase in the number of depth phases detected, particularly for smaller-magnitude events, and makes a substantial difference to the location of seismicity in intraslab settings, and to the resolution of the seismogenic structure of the slab.

Session: Special Applications in Seismology - I

Type: Oral

Date: 5/1/2024

Presentation Time: 05:30 PM (local time)

Presenting Author: Timothy

Student Presenter: No

Invited Presentation: 

Authors