  Widely distributed optical fibers, together with phase-sensitive laser
interferometry, can expand seismic detection methods and have great potential
for epicenter localization. In this paper, we propose an integral response
method based on a forward transmission scheme. It uses spectrum analysis and
parameter fitting to localize the epicenter. With the given shape of the fiber
ring, the integral phase changes of light propagating in the forward and
reverse directions can be used to determine the direction, depth, distance of
the epicenter, and seismic wave speed. For the noisy case with SNR=20 dB, the
simulation results show ultrahigh precision when epicenter distance is 200 km:
the error of the orientation angle is ~0.003{\deg}, the error of the P-wave
speed is ~0.9 m/s, the error of the epicenter depth is ~9.5 m, and the error of
the epicenter distance is ~200 m.
