Speaker
Description
Seismic observations provide information about the Earth's internal structure and its response to transient disturbances. Conventional seismometers provide measurements at discrete locations while coherent laser interferometry applied to deployed telecommunication fibers offers a way to extend seismic observations into sparsely instrumented regions, including the submarine environment.
We report on ongoing work characterising a 260 km submarine optical fiber link between Malta and Sicily (Italy), which reaches a maximum depth of approximately 4 km in the Ionian Sea. Instantaneous optical phase deviations are recorded and interpreted alongside catalogued events and recordings from permanent seismic stations in the region. The interferometric measurements capture distinct components of the seismic wavefield, including P-wave, S-wave and surface-wave arrivals, over a broad range of earthquake magnitudes and distances, with surface-wave trains observed from teleseismic sources. The background noise is dominated by secondary microseisms, with additional wind-related and diurnally varying anthropogenic contributions that influence the detectability of weak local events.
The observation of multiple seismic phases enables the interferometric response to be examined across different components of the seismic wavefield. In particular, the detection of body-wave arrivals from regional events and surface-wave trains from teleseismic events allows this response to be assessed across different propagation distances. Characterising the instrument response to different seismic phases may provide constraints on the relationship between the optical measurement and the propagating seismic wavefield, and on the applicability of the technique to seismic observations.
This study is funded by the European Union under project SENSEI, which aims to transform fiber-optic communication networks into distributed sensors for detecting environmental and geophysical signals, improving monitoring and early warning across Europe (Project ID 101189545).