Exercise 04 Receiver functions will be determined Receiver

Exercise. 04 • Receiver functions will be determined • Receiver functions will be inverted • Receiver functions and surface-wave dispersion will be inverted jointly

Joint Inversion

Rayleigh Wave Sensitivity

RFTN Partials RFTN

Postulated Advantages of Joint Inversion • Receiver function depends upon travel time and fine detail of structure related to conversions • Surface wave is smoothly affected by velocities So • Advantages of one overcome deficiencies of the other

Purpose of models • Assist location by correctly predicting first arrivals • Properly characterize dynamic wavefield to obtain quantitative estimates of source mechanism and strength

Receiver Function Sensitivity to Structure • Perturb simple crust/mantle model • Examine effect of gradient • Design model to have same vertical travel time

Red = sharp / Blue = strong gradient

Gravity Anomaly • Imagine sampling different structures within a region • What would be seen in Bouguer anomaly

180 m. Gal variation among models

Love Rayleigh

Surface waves • Subtle differences in dispersion for fundamental mode in 20 -30 second period range • For surface waves to really contribute structure information, need dispersion for a fine grid of periods • Need short periods to focus on upper crust

Receiver Functions • Slides for different filter parameter - alpha =1. 0 corresponds to a lowpass corner of about 1/3. 14 Hz • Focus on effect of Moho transition on nature of P-wave receiver function

Comments • 1 st peak controlled by shallow structure • Gradient indicated by absence of signal for high alpha, character by low alpha • Sharp moho is indicated by distinct bounce arrivals for all alpha, especially higher • Simultaneous fit to several alpha robust

New Dispersion Data • Harvard group velocities • Colorado group velocities • Phase velocities from Korea – Treat BB network as array – Optionally apply match filter – Apply Mc. Mechan and Yedlin p-tau implemented as sacpom 96

01 Jan 2001 Alaska Event - phase match output used from 10 stations

• • Blue - Colorado Green - Harvard • Orange - Stevens • Red - Korea phase velocity

Receiver functions • Two filter parameters • Stacked RFTN’s • Arranged by similarity in shape • Last 3 are from island stations Similarity in RFTN’s > similarity in structure

Starting Model • AK 135 - depths > 50 km • Upper 50 km is a halfspace with velocity of z=50 km • Invert new dispersion • Use stacked RFTN’s • Use same script

Exercise • cd Exercise. 04 This used pre-existing SAC files. We must worry about the different byte order if the files were created on a SPARC or MAC and then analyzed on a PC. Solution saccvt -I < f. sac > tmp ; mv tmp f. sac

Step 2: rotate to great circle and then pick P more complicated under sac 2000 than gsac

sac 2000 • • • Read three components synchronize for different start, end times save set cut reread save read horizontals rotate read 3 components - pick P

gsac • Read 3 components • rotate 3 components to great circle • pick P • save The script DOPREP automates this

Computation RFTN Use Ligorria and Ammon iterative decon The script DORFTN accomplished this. It also uses the epicentral distance and source depth to get the ray parameter RFTN computed for ALPHA = 0. 5 1. 0 and 2. 5 Radial and transverse RFTN’s are saved.

Inversion tests Directories JOINT. 0. 5 has script for joint inversion using only the ALPHA=0. 5 RFTN Directory JOINT. ALL will use all three ALPHA values. The RFTN. 0. 5 inverts only the RFTN. The purpose of these tests is to get a sense of the sensitivity of the inversion results to the particular data set used.

DOIT. deep • Sets smoothing parameters • Sets weighting, e. g. , do not permit lower part of model to depart from global models of upper mantle • Perform iterative inversion

RFTN

Joint

All models