5.1.3 Crustal structure and Q

A large database can be a good source of information for determining structural parameters and SEISAN provides several programs to determine the crustal structure and Q. Using seismic arrival times, it is possible to invert for the crustal structure using the VELEST program (Kissling et al., 1994). It is also possible to do forward modeling using the location program for a large number earthquakes, since it at the end of a run, a summary of average station travel time residuals and event RMS is given. A special option of HYP is to locate a data set with all permutation of a given range of models in order to find the model giving the lowest RMS.

Deep earthquakes under a local network produce clear phase conversion at crustal interfaces (Chiu et al., 1986). They can be modeled with one of the full wave modeling programs both with respect to amplitude and arrival time.

Attenuation can be determined using the coda Q method for local earthquakes (CODAQ). The coda Q program will calculate q for a series of events and stations at given frequencies. Average values are calculated and a q vs f curve is fitted to the calculated values. The principle for calculation is the standard coda q method, whereby a coda window is bandpass filtered, an envelope fitted and the coda q at the corresponding frequency calculated (Havskov et al., 1989). The SPEC program will determine Q by calculating spectral ratios or the near surface a ttenuation using the spectral decay method. An alternative is to use spectral modeling where Q, stress drop and seismic moment are modeled simultaneously. The AUTOMAG program can do a grid search for find the best attenuation parameters that will fit a series of eartquakes.