Seismic observation and subsurface imaging using an urban telecommunication optic-fiber cable

Seismic observation and subsurface imaging are of key importance in mitigating the seismic hazards exploiting spaces urban areas. However, is, to some extent, hindered by more populations facilities To develop new methods for observation, we carried out several field experiments Binchuan city, Yunnan Province. In experiments, applied distributed acoustic sensing (DAS) technique an telecommunication optic-fiber cable monitor ground motions. The DAS was rapidly developed investigations different scales during past years. city is located basin, which one largest sedimentary basins western Yunnan. basin well studied equipped with instruments, including a Fixed Airgun Signal Transmission Station (FASTS). FASTS can radiate highly repeatable signals energy equivalent magnitude 0.7 earthquake; signal be used test sensitivity instruments seismically quiet period. During experiment, 5.2 km long buried along two local roads parted into ~1000 channels channel spacing meters, vibration continuously digitized sampling rate 5000 sps (samples per second). registered motions originating from various sources. We clearly identified vibrations moving speed ~40 km/h, likely originate vehicles road. fired 111 airgun shots. each single shot invisible records, but emerged after stacking. recorded show similar features as recordings co-located short period seismometers. feasibility DAS, also hammered at 48 points road 8 kg hammer. hammer traveling apparent velocities 300−400 m/s distance ~100 m. Furthermore, reconstructed empirical Green’s function continuous record. able retrieve high-quality surface wave corresponding dispersion curves (the relationship between velocity frequency) 20-min noise recordings. Then based on curves, obtained shear structure uppermost 200 layer important soil classification engineering seismology. m range ~280 430 m/s, indicating class II basin. Our preliminary results revealed using cable, provides novel method many applications, such fine imaging, traffic monitoring, earthquake early warning.