We use data from a small aperture array in southern California to quantify
variations in source parameter estimates at closely spaced stations (distances ranging
from ∼7 to 350 m) to provide constraints on parameter uncertainties. Many studies do
not consider uncertainties in these estimates even though they can be significant and
have important implications for studies of earthquake source physics. Here, we estimate
seismic source parameters in the frequency domain using empirical Green’s function
(EGF) methods to remove effects of the travel paths between earthquakes and their
recording stations. We examine uncertainties in our estimates by quantifying the resulting
distributions over all stations in the array. For coseismic stress drop estimates, we
find that minimum uncertainties of ∼30% of the estimate can be expected. To test the
robustness of our results, we explore variations of the dataset using different groupings
of stations, different source regions, and different EGF earthquakes. Although these
differences affect our absolute estimates of stress drop, they do not greatly influence
the spread in our resulting estimates. These sensitivity tests show that station selection is
not the primary contribution to the uncertainties in our parameter estimates for single
stations. We conclude that establishing reliable methods of estimating uncertainties in
source parameter estimates (including corner frequencies, source durations, and coseismic
static stress drops) is essential, particularly when the results are used in the comparisons
among different studies over a range of earthquake magnitudes and locations.