High density network data is now making it possible to visualize seismic wavefields as time-varying two-dimensional fields at the surface of the earth. This project uses the Southern California Seismic Network with station contributions from AMOES, USGS, and TERRASCOPE. The study area incorporates stations from 37.5 degrees latitude to 32.5 degrees latitude and from -114 degrees longitude to -120 degrees longitude. There are many benefits of analyzing data in 2D instead of 1D, such as ease in visualization of wave propagation in areas of high complexity and the ability to see the spatial extent of seismic disturbances directly.

Initially we used a 2D direct B-spline method to approximate the wavefield. This method failed primarily due to insufficient network density for the frequencies of interest. For this method the minimum wavelength that can be reasonably recovered is 100-150 kilometers; however P-waves require resolution of wavelengths between 50-60 kilometers even for filtered long period signals( period of 10 seconds ). This method had to be modified to the present method which uses the azimuth of arriving wavepackets, its apparent velocity, and approximate waveform from the same data to create a reference wavefield. This reference wavefield fits the data reasonably well and the misfit can be fitted using cubic B-splines. This method works due to the fact that the misfit consists mostly of long period wavelengths. At the moment this method works for telesiesmic events and not yet for local events.

EVENT NUMBER:
990817000140

MAGNITUDE:
7.6Mw

LOCATION:
Izmit, Turkey
40.5 Lat, 29.6 Lon.

Check out the station map for coverage details. Notice the large resonating peak in the vicinity of the LA Basin.