Temporal variations of velocity structure in the Tatun Volcano Group, Northern Taiwan

The Tatun Volcano Group (TVG) is an active volcano situated near a densely populated area with over 7 million residents. Given the existence of risk regarding volcanic activities, a dense seismic network has been deployed in the TVG by the Taiwan Volcano Observatory at Tatun. We used the observed seismic data to invert the yearly velocity model from 2014 to 2021. After a series of careful examinations, we constructed a 4D seismic velocity model in the TVG. Then we found the velocity model has the significant variations beneath the Dayoukeng where the helium isotope ratio (³He/⁴He) is approaching 7. Additionally, the area with significant variations of seismic wave velocity is located at the plausible pathway of volcanic fluids from deep to near surface in the TVG. Therefore, we consider that the temporal variations of velocity structures are associated with the local activities of volcanic fluids in the TVG.