Crustal and upper mantle structure beneath the Katmai Volcanic Cluster, Alaska, from receiver functions

The crustal and upper mantle structure beneath the Katmai Volcanic Cluster, Alaska, was imaged using receiver function (RF) analysis of 774 teleseismic events recorded on broadband station KABU between March 2005-July 2011. All events were sorted by backazimuth (BAZ) into 10° bins, and RFs computed using the multiple-taper spectral correlation estimate technique. This technique involves the deconvolution of the vertical component from the radial and transverse components in the frequency domain to isolate the P-S converted phases in the P-wave coda. Preliminary analysis of radial RFs with BAZ 0°-70° reveals a negative phase at 2 s with an increase in amplitude of this phase with increasing BAZ; a positive phase at 3 s, again with an increase in amplitude with increasing BAZ; and a double negative phase between 4-10 s. The high amplitude transition from a negative (2 s) to a positive (3 s) phase indicates layers with a high impedance contrast, suggesting a transition from a high velocity layer to a low velocity layer. The depth of the transition between these phases is estimated at ~16-21 km. The transition from the positive phase (3 s) to the double negative phase (4-10 s) is estimated to occur at ~29-33 km, consistent with independent estimates of the depth to the Moho in this area. Transverse RFs show energy at all BAZ, indicating a high degree of heterogeneity, as is expected in volcanic areas. Preliminary forward modeling suggests two low velocity zones beneath station KABU; however additional data analysis and a formal inversion is needed to confirm this model. RFs in the 300°-360° BAZ show a high degree of complexity which may be due to the raypath of the events parallel to the volcanic arc.