Abstract
Abundant earthquakes clustered within a particular zone often reflect an active geological feature, such as clustering seismicity along a fault zone and a huge number of volcanic-earthquakes around the erupting conduit. Herein we perform a double-difference tomographic inversion and relocate the seismicity at the long-resting Tatun volcano group (TVG) in northern Taiwan. A dramatic improvement of the earthquake location model surprisingly show that, from 2014 to 2017, two clustered seismic zones are identified in the TVG. One major group of events (>1000) persistently clustered within a ~500 m diameter vertical conduit with a ~2 km height. The clustering seismicity conduit is just located nearby Dayoukeng, one of the strongest fumaroles in the TVG, and is connected to a fracture zone characterized by low Vp/Vs in the shallow crust. The other group of events is clustered within a sphere-like zone beneath Mt. Chihsin around the depths between 0.5 km and 2 km. Both seismic zones are probably triggered by the significantly volcanic gases and fluids ascending from the deep magma reservoir. Combined with a variety of results from literature, the seismicity conduit near the strong fumarole is the evidence for an active volcano and also identifies a likely pathway for ascending magma if the TVG erupts again in the future. But possibility of developing different magma pathways at other clustered seismic zones such as beneath Mt. Chihsin may not be totally excluded.
Highlights
The evaluation of whether or not a volcano will erupt often relies on the classification of it as active, dormant, or extinct; the exact definition of an active volcano may still be debatable
From the volcanic hazard point of view, it is important to know whether or not the Tatun volcano group (TVG) is active because it is located near the Taipei metropolis, with more than 6 million residents living in both Taipei City and New Taipei City in northern Taiwan (Fig. 1)
We produce seismic tomographic images based on the P- and S-wave arrival time data recorded at 40 broadband seismic stations in the TVG area between 2014 and 2017
Summary
The evaluation of whether or not a volcano will erupt often relies on the classification of it as active, dormant, or extinct; the exact definition of an active volcano may still be debatable. The 3-D velocity structures of P-waves (Vp), S-waves (Vs) and the ratios between both (Vp/Vs) at depths shallower than 5 km can successfully be inverted by the double-difference tomography[17] These tomographic images allow us to improve the understanding of the volcanic plumbing system in the shallow crust beneath the TVG. The relocated seismicity interestingly shows a vertical conduit within a ~500 m diameter area near the Dayoukeng fumarole, one of the strongest degassing processes in the TVG, at a depth between ~0.2 to 2 km below the surface Such a seismicity conduit is the major pathway for the transport of volcanic gases and fluids from deep reservoirs to the surface; it may be one of the most likely pathways for ascending magma for TVG eruptions in the future. Chihsin is the highest peak and probably the youngest volcano in the TVG15 and the Dayoukeng fumarole is one of the strongest degassing processes in the TVG [12; supplemental video]
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