P wave amplitudes in 3D Earth Guust Nolet, Caryl Michaelson, Ileana Tibuleac, Ivan Koulakov, Princeton University The objective: Assess the possibility of incorporation of focusing/defocusing effects by lateral heterogeneity in the tomographic inversions Method Compare a set of amplitude variations from deep earthquakes to predicted amplitude variations by 3D global models DATA n 29 events recorded by IRIS GSN n January May 2000 n 5.6 < mb < 7.6 n Depth 88 km km n deg epicentral distance Hand picked P arrivals on vertical component of broadband instruments Method We measured: -maximum zero-to-peak amplitude -maximum peak-to-peak amplitude -integrated amplitude over pulse duration -integrated squared amplitude over the pulse duration on raw and 0.2 Hz low pass filtered data We excluded stations/events with: -interference of P and another phase -low SNR -short pulse duration ( < 2 sec) -bad fit of polarity predicted by CMT solution Method Volcano Islands Region event, 03/28/2000, mb=7.6, km deep Stack of P wave pulse Method Theoretical expression for the P wave energy: E = S 2 R 2 G- 2 a s a r S - source term from Harward CMT solution R - free surface effect at the receiver G- 2 - geometrical spreading coefficient calculated for a particular model a s a r - source and receiver corrections respectively Method Can we use frequency independent correction factors? Ray tracing results event 1999/07/21, 13:46, mb =5.6, 175 km depth Ray tracing results event 2000/03/28, 11:00, mb =7.6, km depth Results Results raw data Results low pass filter 0.2 Hz Results Raw data Low pass 0.2 Hz Conclusions Causes for the misfit observed - predicted energy: 3D attenuation in the upper mantle Attenuation in the lower mantle Variation of instrument gain Frequency dependence of correction factors Complex radiation patterns Strong focusing and defocusing by 3D structure Conclusions What we think about them: Absorbed in the correction factors Not strong enough for observed variations of up to 50% less than 5% Small for frequencies < 0.5 Hz Wavelength of P waves was comparable to the fault size for most of the events that must be it but Conclusions What we think about them: Absorbed in the correction factors Not strong enough for observed variations of up to 50% less than 5% Small for frequencies < 0.5 Hz Wavelength of P waves was comparable to the fault size for most of the events that must be it but Conclusions The actual tomographic models fail to explain the misfit in observed and calculated energy because the predicted focusing is too small