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This study analyzed time series data from six GPS stations within the Tatun Volcano Group (TVG), a long‐dormant volcanic system in northern Taiwan, using multichannel singular spectrum analysis to search for potential spatiotemporally correlated transient deformations. A notable cycle of transient deformation was identified from 2015 to 2020, characterized by ground subsidence and uplift of up to 10 mm, accompanied by asymmetric horizontal motions directed inward and outward toward Dayoukeng, the largest fumarole and hydrothermal area in TVG. Evidence from earthquake focal mechanisms and gas composition, along with preliminary source modeling, suggest that these transient phases were likely caused by the pressure change of shallow hydrothermal systems beneath Dayoukeng. Further analysis of time series data from three long‐operating GPS stations revealed similar patterns of transient motion in the area from 2006 to 2015, indicating that TVG has experienced cyclical deformation, akin to many other volcanic systems worldwide. Plain Language Summary: Monitoring ground deformation in volcanoes is crucial for understanding the underlying processes and providing early warnings of potential hazards. Previous geodetic studies of the long‐dormant Tatun Volcano Group (TVG) in northern Taiwan relied on sporadic data, leading to incomplete insights into its time‐varying deformation behavior. Continuous GPS, however, allows for accurate tracking of surface movements over time, including short‐term changes caused by intermittent volcanic activity. This first GPS study of TVG employed a method called multichannel singular spectrum analysis to identify transient signals in noisy data from six stations. Significant ground deformation was revealed between 2015 and 2020, with the ground sinking and rising by up to 10 mm, along with horizontal movements toward and away from Dayoukeng, a major steam vent area in TVG. This sinking is likely related to changes in the shallow hot water and steam systems beneath Dayoukeng, as suggested by anomalies in earthquake activity and surface gas composition. Additional GPS data from 2006 to 2015 revealed that TVG experienced recurring cycles of ground deformation, closely correlated with local seismic activity. Key Points: Data‐adaptive detection of transient deformation in noisy GPS time seriesCycle of ground deformation first detected in the Tatun Volcano area, where about 7 million people reside nearbyHydrothermal processes may have driven consistent spatiotemporal variations in seismicity and deformation in the Tatun Volcano area [ABSTRACT FROM AUTHOR]

We test the feasibility of GPS-based rapid centroid moment tensor (GPS CMT) methods for Taiwan, one of the most earthquake prone areas in the world. In recent years, Taiwan has become a leading developer of seismometer-based earthquake early warning systems, which have successfully been applied to several large events. The rapid determination of earthquake magnitude and focal mechanism, important for a number of rapid response applications, including tsunami warning, is still challenging because of the limitations of near-field inertial recordings. This instrumental issue can be solved by an entirely different observation system: a GPS network. Taiwan is well posed to take advantage of GPS because in the last decade it has developed a very dense network. Thus, in this research, we explore the suitability of the GPS CMT inversion for Taiwan. We retrospectively investigate six moderate to large (M w6.0 ∼ 7.0) earthquakes and propose a resolution test for our model, we find that the minimum resolvable earthquake magnitude of this system is ∼ M w5.5 (at 5 km depth). Our tests also suggest that the finite fault complexity, often challenging for the near-field methodology, can be ignored under such good station coverage and thus, can provide a fast and robust solution for large earthquake directly from the near field. Our findings help to understand and quantify how the proposed methodology could be implemented in real time and what its contributions could be to the overall earthquake monitoring system. [ABSTRACT FROM AUTHOR]

The M w 5.9 Wutai earthquake of 26 February 2012 occurred at a depth of 26 km in southern Taiwan, where the rupture is not related to any known geologic structures. To illustrate the rupture source of the mainshock, we employ an elastic half-space model and GPS coseismic displacements to invert for optimal fault geometry and coseismic slip distribution. With observations of both coseismic horizontal and vertical displacements less than 10 mm, our preferred fault model strikes 312° and dips 30° to the northeast and exhibits a reverse slip of 28–112 mm and left-lateral slip of 9–45 mm. Estimated geodetic moment of the Wutai earthquake is 1.3 × 10 18 N-m, equivalent to an M w 6.0 earthquake. The Wutai epicentral area is characterized by a NE–SW compression as evidenced by the slaty cleavage orientations and the interpretation of stress tensor inversion of earthquake focal mechanisms. Using the stress drops of the Wutai and the nearby 2010 M w 6.4 Jiashian earthquakes, we obtain a lower bound of ~ 0.002 for the coefficient of friction on the fault. On the other hand, studying the crustal thickness contrast in southern Taiwan provides an upper bound of the average horizontal compressive force of 1.67 × 10 12 N/m transmitted through the Taiwan mountain belt and gives an estimate of the maximum friction coefficient for 0.03. The deviation of an order of magnitude difference between the upper and lower bounds for the coefficient of friction suggests that other fault systems may support substantial differential stress in the lithosphere as well. [ABSTRACT FROM AUTHOR]

The Lishan fault has been characterized alternately as a major discontinuity in stratigraphy, structures and metamorphism, a ductile shear zone, a tectonic suture or non-existent. In addition to being a geological boundary, it also marks transitions in subsurface structures. Thus, the seismicity to the west of the fault permeates through the upper and mid-crust while beneath the Central Range it is noticeably less and largely concentrated in the upper 12 km. A prominent west-dipping conductive zone extends upward to meet the Lishan fault. Also, the eastward increase of crust thickness from ~ 30 km in the Taiwan Strait quickens under the Lishan fault to form a root of over 50 km under the Central Range. In the past, the small magnitude seismicity along the Lishan fault has been noticed but is too diffuse for definitive association with the fault. Recent processing of aftershock records of the 1999 Mw 7.6 Chi-Chi earthquake using Central Weather Bureau data and, especially, data from three post-Chi-Chi deployments of seismic stations across central Taiwan yielded hypocenters that appear to link directly to the Lishan structure. The presence of a near 4-km-long vertical seismic zone directly under the surface trace of the Lishan fault indicates that it is an active structure from the surface down to about 35 km, and the variety of focal mechanisms indicates that the fault motion can be complex and depth-dependent. [ABSTRACT FROM AUTHOR]

Abstract: Integration of geophysical and geological data show that the Yellowstone hotspot resulted from a mantle plume interacting with the overriding North America plate, a process that has highly modified continental lithosphere by magmatic and tectonic processes and produced the 16-17Ma, 700-km-long Yellowstone-Snake River Plain (YSRP) silicic volcanic system. Accessibility of the YSRP allowed large-scale geophysical projects to seismically image the hotspot and evaluate its kinematic properties using geodetic measurements. Seismic tomography reveals a crustal magma reservoir of 8% to 15% melt, 6km to 16km deep, beneath the Yellowstone caldera. An upper-mantle low-P-wave-velocity body extends vertically from 80km to 250km beneath Yellowstone, but the anomalous body tilts 60°WNW and extends to 660km depth into the mantle transition zone. We interpret this conduit-shaped low-velocity body as a plume of up to -3.5% Vp and -5.5% Vs perturbation that corresponds to a 1-2% partial melt. Models of whole mantle convection reveal eastward upper-mantle flow beneath Yellowstone at relatively high rates of 5cm/yr that deflects the ascending plume into its west-tilted geometry. A geodynamic model of the Yellowstone plume constrained by Vp and Vs velocities and attenuation parameters suggests low excess temperatures of up to 120K, corresponding to a maximum 2.5% melt, and a small buoyancy flux of 0.25Mg/s, i.e., properties of a cool, weak plume. The buoyancy flux is many times smaller than for oceanic plumes, nonetheless, plume buoyancy has produced a ~400-km-wide, ~500-m-high topographic swell centered on the Yellowstone Plateau. Contemporary deformation derived from GPS measurements reveals SW extension of 2-3mm/yr across the Yellowstone Plateau, one-fourth of the total Basin-Range opening rate, which we consider to be part of Basin-Range intraplate extension. Locally, decadal episodes of subsidence and uplift, averaging ~2cm/yr, characterize the 80-year Yellowstone caldera monitored history and are modeled as hydrothermal-magmatic sources. Moreover a recent episode, 2004-2009, of accelerated uplift of the Yellowstone caldera at rates up to 7cm/yr has been modeled as resulting from magmatic recharge of a 10-km-deep sill at the top of the crustal magma reservoir. Regionally, gravitational potential energy of the Yellowstone swell drives the lithosphere southwest and “downhill” from the Yellowstone Plateau 400km where it coalesces with Basin-Range province-wide westward extension. Based on the geometry and its assumed 660km depth, we extrapolate the plume source southwest to its original location at 17Ma and 600km southwest and 200km north of the YSRP. Importantly, this location is beneath the southern part of the Columbia Plateau flood basalt field of the same age and implies that the Yellowstone mantle plume may be the common source for both of these large volcanic fields. Our time-progression model suggests that the original plume head rose vertically behind the Juan de Fuca plate, but at ~12Ma it lost the protection of the subducting plate from eastward mantle flow and encountered cooler, thicker continental lithosphere, becoming entrained in eastward upper-mantle flow. These results reveal that Yellowstone plume-plate processes have had a profound effect on Late Cenozoic geologic evolution and topography of a large part of the western U.S. [Copyright &y& Elsevier]

Geoelectric self‐potential (SP) signals are sensitive to natural and anthropogenic factors. The SP spectral characteristics under the different factors in Taiwan were investigated, and the SP spectral scalings were correlated with urbanization level, seismicity, and crustal deformation. The ambient SP noise models were first established by estimating the probability density functions of the spectrograms at each frequency. The effects of the natural and anthropogenic factors on the SP signals are understood by comparing the SP noise models under various conditions, such as precipitation, urbanization, and electric trains. Results show that the SP signals in areas of high industrialization and human activity and areas close to train stations behave as white noises and exhibit a distinct spectral ripple at frequencies around 1 Hz. On the other hand, the SP spectral power law parameters, Gutenberg‐Richter b values, and dilation strain rates were estimated by using the SP, earthquake catalog, and GPS data, respectively, during 2012–2017. By investigating the correlations of the SP spectral parameters with the Gutenberg‐Richter b value, dilation strain rates, and urbanization level, the SP optimal frequency band is found between 0.006 and 1 Hz due to the high correlation between the SP and seismicity data and between the SP and dilation data and the low correlation between the SP and urbanization data. Hence, this study may help the filtering and screening of the SP data and facilitate the understanding of the mechano‐electric behavior in the crust. Plain Language Summary: Self‐potential is a naturally electric potential difference beneath the Earth's surface, measured between any two points on the ground or in boreholes. The self‐potential signals are sensitive to natural factors, such as ionospheric disturbance, solar wind, and tidal forces, and to artificial factors, such as electric trains, factories, and power pipelines. Hence, the investigation of the background noises is critical. The self‐potential noise models were established by estimating the probability density functions of the daily power spectral densities. We compared the noise models under several conditions, such as urbanization, electric trains, and rainfalls. We found that the noise models behave as white noises in areas of high industrialization and human activity. Furthermore, we also estimated the self‐potential power law parameters, seismic b values, and dilation strain rates. We then studied correlations of the self‐potential power law parameters with the urbanization levels, b values, and dilation strain rates. We found out the frequency‐dependent correlations of the spectral scalings with the other parameters and determined the self‐potential signals with a high signal‐to‐noise ratio in the frequency band of 0.006–1 Hz. Understanding such correlations may understand the feature of the mechano‐electric behavior in the crust and facilitate the development of a seismic‐electric theory. Key Points: Self‐potential (SP) signals show white noises or spectral ripples in areas of high industrialization and areas close to train stationsThe SP spectral exponent seems to positively relate to the seismic b value and dilation rate and negatively to the urbanization levelThe SP spectral exponent shows frequency‐dependent correlations with the seismic b value, dilation rate, and urbanization level [ABSTRACT FROM AUTHOR]