We use seismic ambient noise recorded by ocean bottom nodes (OBNs) in
the Gorgon gas field, Western Australia to compute time-lapse seafloor
models. The extracted hourly cross-correlation (CC) functions of 0.1 –
1 Hz contain mainly Scholte waves with very high signal to noise ratio.
The conventional time-lapse analysis suggests relative velocity
variations (dv/v) up to 1% assuming a spatially homogeneous dv/v, with
a likely 24-hour cycling pattern. With high-resolution baseline models
from full waveform inversion of Scholte waves, we propose a
double-difference waveform inversion (DD-WI) method using travel time
differences for localizing the time-lapse dv/v in the heterogeneous
subsurface in depth. The time-lapse velocity models show velocity
increase/decrease patterns in agreement with that from conventional
analysis, with more notable changes at the shallower depths. We
demonstrate the feasibility of using ambient noise for quantitative
monitoring of subsurface property changes in the horizontal and depth
domain at an hourly basis.