3-D Empirical travel times for global heterogeneity
Abstract
Many applications in seismology rely on the accurate prediction of teleseismic travel times. As an alternative to travel time calculation in 1-D or 3-D seismic velocity models, we have developed a new approach based on directly smoothing and interpolating observations from large earthquake catalogues. We call the approach 3-D Empirical Travel Times (ETT). This approach is able to handle both the spatial variability in data density, as well as the many length scales of heterogeneity that influence observed travel times. An important feature of the technique is that after the empirical travel time corrections have been applied the remaining residuals are spatially uncorrelated and, in this sense, all of the signal in the data is accounted for. Travel times predicted with the new approach compare very favourably with those from 1-D and 3-D Earth models. Travel time residuals of nuclear blast data are reduced by 62%, on average, compared to 1-D reference Earth models. Tests with globally distributed earthquake data give an average residual reduction of up to 42% across a range of teleseismic phases. Tests also show that, 3-D empirical travel times reproduce the pattern of regional variation in tele-seismic phases very well. In epicentre determination of 25 nuclear blasts, the use of empirical travel times in place of 3-D global velocity models reduced the average mislocation by over 59%. The new approach can also be used for `denoising' travel times from large earthquake databases, giving a new `data source' for tomographic studies. Although developed for use in teleseismic studies, the empirical travel time approach has the flexibility to be applied to local or regional seismicity. This model free `database' approach to travel time prediction results in a highly accurate and robust method and in a sense a return to the empirical philosophy of Jeffreys and Bullen (1940). It is likely to find applications in a range of seismological problems.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....4420N