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Cloud-to-ground lightning can cause high-temperature and high-pressure deformation features in rock at the strike point, forming fulgurite. Although cloud-to-ground lightning is a frequent phenomenon, rock fulgurites are rarely reported. Here, we present field, optical microscope, X-ray fluorescence, scanning and transmission electron microscope, in situ synchrotron projection X-ray microscopy and X-ray diffraction, and Raman data to investigate the formation and preservation of a recently formed rock fulgurite from Kinmen Island, Taiwan. In the field, the fulgurite is asymmetrically distributed on the surface over an ~ 12 m2 area. In detail, the fulgurite contains an opaque glassy layer comprised of quartz and feldspar clasts, voids, iron-rich spheres, and barite aggregates that overlies fractured quartz grains and feldspar grains with planar features. Secondary minerals found locally adhering to the glassy layer as greenish patches are mainly jarosite group minerals, which commonly form as a secondary hydrothermal alteration product. We interpret the jarosite to have formed during the solidification of melt in the presence of raindrops, suggesting the rapid alteration of glass and short preservation potential of rock fulgurite. Finally, we estimate the production ratio of fulgurite by calculating the energy required for fulgurite formation and that released to the ground by the lightning event. A calculated energy ratio of 0.026% is within the range of 10–2 to 10–4 of the lightning total energy delivered to the strike point. We suggest that the scarcity of rock fulgurite in the geological record may be due to both the low production possibility and rapid alteration. [ABSTRACT FROM AUTHOR]

In this paper we test whether or not structural and morphological features inherited from the Eurasian continental margin are affecting the contemporary stress and strain fields in south-central Taiwan. Principal stress directions (σ1, σ2 and σ3) are estimated from the inversion of clustered earthquake focal mechanisms and the direction of the maximum compressive horizontal stress (S H) is calculated throughout the study area. From these data the most likely fault plane orientations and their kinematics are inferred. The results of the stress inversion are then discussed together with the directions of displacement, compressional strain rate and maximum shear strain rate derived from GPS data. These data show that there is a marked contrast in the direction of S H from north to south across the study area, with the direction of S H remaining roughly subparallel to the relative plate motion vector in the north, whereas in the south it rotates nearly 45° counter-clockwise. The direction of the horizontal maximum compression strain rate (εH) and associated maximum shear planes, together with the displacement field display an overall similar pattern between them, although undergoing a less marked rotation. We interpret the southward change in the S H, εH and the dextral maximum shear plane directions, together with that of the horizontal displacement field to be related to the reactivation of east–northeast striking faults inherited from the rifted Eurasian margin and to the shelf/slope break. Inherited faults in the basement are typically reactivated as strike-slip faults, whereas newly formed faults in the fold-and-thrust belt are commonly thrusts or oblique thrusts. Eastwards, the stress inversions and strain data show that the western flank of the Central Range is undergoing extension in the upper crust. S H in the Central Range is roughly parallel to the relative plate convergence vector, but in southwestern Taiwan it undergoes a marked counter-clockwise rotation westwards across the Chaochou fault. Farther north, however, there is no significant change across the Lishan fault. This north to south difference is likely due to different margin structures, although local topographic effects may also play a role. [ABSTRACT FROM AUTHOR]

A thorough understanding of the internal structures of the Longitudinal Valley is crucial for comprehending the architecture of the suture zone between the Eurasian and Philippine Sea plates. Here, we present the findings of eight new reflection seismic profiles spanning north to south of the Longitudinal Valley. Our primary objective is to investigate the internal sedimentary and tectonic features of the Longitudinal Valley Basin, the nature of the contact between it and the metamorphic basement rocks to the west, and the geometry of the Longitudinal Valley fault system along its eastern flank. A significant outcome of our research is that there is minimal internal deformation within the Longitudinal Valley Basin, with sedimentary features prevailing. The presence of inclined reflections suggests the presence of fan deltas and therefore a marine or lacustrine environment in the Longitudinal Valley. The sedimentary characteristics indicate that the source region for the sediment was predominately the Central Range, but that locally the Coastal Range also supplied sediment. Furthermore, at least in the shallow subsurface (1 to 2 km), a west-dipping Central Range fault does not exist along the western side of the Longitudinal Valley. The Longitudinal Valley fault system does not affect the middle of the basin, instead it is located along the eastern flank, adjoining the topography of the Coastal Range. • Eight new reflection seismic profiles across Taiwan's Longitudinal Valley Basin. • A west-dipping Central Range fault is not imaged along the western side of the basin. • The Longitudinal Valley fault is imaged along the eastern flank of the basin. • Minimal internal deformation within the basin, with sedimentary features prevailing. • Clinoforms suggest marine or lacustrine environments in the Longitudinal Valley. [ABSTRACT FROM AUTHOR]

The Taiwan mountain belt is generally thought to develop above a through-going basal thrust confined to within the sedimentary cover of the Eurasian continental margin. Surface geology, magnetotelluric, earthquake hypocenter, and seismic tomography data suggest, however, that crustal levels below this basal thrust are also currently being involved in the deformation. Here, we combine seismic tomography and earthquake hypocenter data to investigate the deformation that is taking place at depth beneath south-central Taiwan. In this paper, we define the basement as any pre-Eocene rifting rocks, and use a P-wave velocity of 5.2 km/s as a reference for the interface between these rocks and their sedimentary cover. We found that beneath the Coastal Plain and the Western Foothills clustering of hypocenters near the basement-cover interface suggests that this interface is acting as a detachment. This detachment is located below the basal thrust proposed from surface geology for this part of the mountain belt. Inherited basement faults appear to determine the geometry of this detachment, and their inversion in the Alishan area result in the development of a basement uplift and a lateral structure in the thrust system above them. However, across the Shuilikeng and the Chaochou faults, earthquake hypocenters define steeply dipping clusters that extend to greater than 20 km depth, above which higher velocity basement rocks are uplifted beneath the Hsuehshan and Central ranges. We interpret these clusters to form a deeply penetrating, east-dipping ramp that joins westward with the detachment at the basement-cover interface. It is not possible to define a basal thrust to the east, beneath the Central Range. [ABSTRACT FROM AUTHOR]

On 27 March 2013, a 6.2 ML earthquake occurred at 19 km depth in eastern Nantou, central Taiwan. Over a 2 week period it was followed by more than 680 aftershocks that ranged to 5 ML. Most events occurred below the ~10-km-deep detachment fault predicted for this part of the mountain belt, coinciding with other precisely located hypocenters that indicate that much of the crust in this area is seismically active. We combine geological data with a three-dimensional (3-D) P-wave velocity model derived from local tomography and earthquake hypocenters to determine a model for the structure of central Taiwan. Much of the surface geology of the area comprises the uplifted Eocene rocks of the Hsuehshan Basin. The 3-D P-wave velocity model shows a shallowing of higher velocities across the Hsuehshan Basin and hypocenter data indicate that its western bounding fault is clearly defined by an eastward-dipping band of events that extends to >20 km depth. The eastern bounding fault is interpreted to coincide at depth with a cluster of events between 20 and 30 km depth. These data suggest that the preexisting, rift-related extensional faults of the Hsuehshan Basin are currently being reactivated and the basin is being inverted. We present hypocenter data from the Nantou sequence that corroborate this interpretation and show the importance of choosing the correct structural model when assessing seismic risk. [ABSTRACT FROM AUTHOR]

Active mountain belts in monsoonal climates are characterized by rapid denudation due to erosion and mass wasting processes. In such areas, unstable topography caused by local geological conditions combined with extreme rainfall or earthquakes impact on indigenous people, especially through involuntary settlement migration. Anthropological surveys in southern Taiwan show that the oral traditions of indigenous people preserve records of natural disasters that took place several hundred years ago. When combined with geological data, these stories allow us to assess the triggers and underlying causes that led to settlement migrations. These settlements are located in the Central Range of southern Taiwan, a high-relief terrain comprised of Miocene formations characterized by well-developed slaty cleavage (S 1) that forms dip slopes that are prone to landslides. Here, we investigate how extreme events coupled with the geological setting caused two relocations of a settlement of the Paiwan group within approximately 350 years. We also draw attention to the point that the oral traditions of indigenous groups can provide important data sets for reconstructing landslides in the recent past (less than 500 years) which other, more traditional methods (e.g. digital data archives) do not record. We conclude that extreme weather provides the trigger, and local geological conditions the underlying factors, for natural disasters that have had a significant impact on the indigenous people in southern Taiwan. • Indigenous people's oral traditions and regional geology can be used to investigate effects of extreme weather. • Regional geology and site investigations of the ancient villages identify the possible causes of settlements migrations. • Extreme weather events and natural disasters may have important socio-economic impact on the indigenous peoples. • Indigenous peoples oral stories is a potential source as supporting data for variety studies as paleoenvironment reconstruction. [ABSTRACT FROM AUTHOR]