We have three events in the Celebes Sea south of Philippine that have virtually the same epicenter. So presumably these would yield equal or at least similar paths to our stations.



In details, events locations are:




The ray-paths are projected to be indeed of uniform trajectory. Where we have basically a single path to each station from all three events.



arrivals and residuals

We would like to compare the residuals out of these three events i.e. the differential time of predicted ak135 model and observed arrival.

We will pick the arrival and find the residual by computing the time between that picked time (blue line) and predicted time (red line). We would expect them to be fairly close to one another for each respective station.



The results are combined in a spreadsheet:




Of course since the depth of the event is not exactly the same, this yields to a difference of two seconds for the amount of time it took to reach the stations. We think this is a reasonable difference in consideration.

The observed arrivals are all late arrivals in respect to the predicted arrivals. Value wise, the differences in residuals between events are fairly consistent.

inversion and misfit

We proceed with the inversion using this data. Regularization is turned on. It seems that the most satisfying result is obtained by making the damping in the regularization to equal zero. While we do so, smoothing need only to have a factor of 1 to have this progression in misfit.



The model correspond to this inversion steps is the following.



The negative anomaly is completely expected considering all of our arrival are late with respect to the 1D-Earth model.