Active Volcanism Revealed from a Seismicity Conduit in the Long-resting Tatun Volcano Group of Northern Taiwan

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 spherelike 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. The evaluation of whether or not a volcano will erupt often relies on the classification of it as active, dormant, or extinct; however, the exact definition of an active volcano may still be debatable. Two criteria are often employed to classify an active volcano: (1) the volcano erupted within the past ~10,000 years or (2) the identification of magma chambers beneath the volcano 1. However, those definitions are not set in stone because some eruptions have surprisingly occurred in dormant or extinct volcanoes, which are long-resting volcanoes without evidence of any magma chambers beneath them. Thus, some other criteria may be involved in the evaluation of the possibility of eruptions in long-resting volcanoes, in particular. The Tatun volcano group (hereinafter "TVG") in the northern tip of Taiwan is a typical long-resting volcano because there was no eruption record in human history. From the volcanic hazard point of view, it is important to know whether or not the 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). The distance between Mt. Chihsin (the highest peak of 1120 m in the TVG) and the Taipei 101 skyscraper building (a landmark in downtown of Taipei City 2) is less than 15 km. In other words, the TVG is a typical "City on Volcano" case if it is active. Apart from the Taipei metropolis, it is worth highlighting the two nuclear power plants located around the northern boundary of the TVG. Thus, even a small volcanic eruption at th...

Lateral Variations of Moho Depth and Average Crustal Properties Across the Taiwan Orogen From H‐V Stacking of P and S Receiver Functions

“…Though no eruptions have been recorded since the latest youngest age (∼0.2 Ma) of the lavas dated in the NTVZ (Wang et al., 2004), the hydrothermal activities such as hot springs and fumaroles are common in the Tatun volcanic area. While still remaining controversial, the paradigm for a ∼30 km‐deep magma reservoir that may exist beneath the Chinshan area between the TVG and KVG has been recently emerged by seismic observations of S‐wave shallows (Lin, 2016) and a shallow, subvertical earthquake‐clustered conduit (Pu et al., 2020). As the melt would reduce V s much more than V p thus increasing V p / V s significantly, a high V p / V s anomaly is usually considered as an indication of potential magma chambers in the volcanic areas.…”

Mantle wedge diapirs detected by a dense seismic array in Northern Taiwan

“…One is the Tatun Volcano Group (TVG) nearby the Taipei metropolitan area, and the other is Kueishantao (or Turtle Island), named for its shape, offshore from the Ilan plain of northeastern Taiwan. Despite the absence of eruption records in human history, both volcanoes have been recognized as active based on a variety of recent observations including Helium isotope analyses 25 , dating of volcanic ashes 26 , seismic detection of magma reservoirs 27 , 28 , and some other interesting seismic activities such as heartbeat-like seismicity 29 , VLP tremors 30 , infrasonic signals 31 , and many others 32 , 33 . Thus, more detailed investigation of both volcanoes becomes very important in Taiwan since potential volcanic impacts cannot be totally excluded in the future.…”

Dense seismic arrays deny a massive magma chamber beneath the Taipei metropolis, Taiwan

“…This finding implies the attenuation in the TVG might result from shallow fracture conduits or the hydrothermal reservoir below them. Such a shallow hydrothermal reservoir and conduits with depths above 3 km have been confirmed by low Rayleigh wave phase velocity 22 , anomalous P-wave delays 23 , and clusters of seismicity 24 . In contrast, further westward away from the geothermal field and the Shanchiao fault, no anomalous or can be found, including at the stations YC03 (Figs.…”