Absolute Earthquake Locations with Differential Data

Not withstanding the commonly-held wisdom that “you can’t determine the absolute location of earthquakes using the double-difference method”, you can. We present a way of visualizing double-difference data, and use it to show how differential arrival time data can, in principle, be used to determine the absolute locations of earthquakes. We then analyze the differential form of Geiger’s Method, which is the basis of many doubledifference earthquake location algorithms, and show that it can be used to make estimates of the absolute location of earthquake sources. Finally, we examine absolute location error in one earthquake location scenario using Monte Carlo simulations that include both measurement error and velocity model error, and show that the double-difference method produces absolute locations with errors that are comparable in magnitude, or even less, than traditional methods. Absolute earthquake locations that are already routinely produced by most implementations of the double-difference method have a better accuracy than has been credited.