The Interrelationships between Faulting and Volcanism in the Okataina Volcanic Centre, New Zealand

<p>Continental rifts show close spatial relations between faulting and volcanism, however the interrelations between each process and their roles in the accommodation of regional extension are not well understood. The geometric and kinematic relations between an active silicic caldera complex and active faults in the upper 3-4 km of the crust (i.e. Taupo Rift) are investigated using regional gravity data, digital elevation models, outcrop mapping, seismic reflection lines, focal mechanisms and an historical account of the 1886 AD Tarawera eruption adjacent to, and within, the Okataina Volcanic Centre, New Zealand.The location and geometry of the Okataina Caldera were influenced by pre-existing faults. The caldera is elongate north-south, has a maximum subsidence of 3 +/- 0.5 km at the rift axis and occupies a 10 km hard-linked left step in the rift. The principal rift faults (55-75 degrees dip) define the location and geometry of the northwest and southeast margins and locally accommodate piecemeal caldera collapse. Segments of the east and west margins of the caldera margin are near vertical (70-90 degrees dip), trend north-south, and are inferred to be faults formed by the reactivation of a pervasive Mesozoic basement fabric (i.e. bedding, terrane boundaries, and/or faults). Measured displacements along the Paeroa and Whirinaki Fault zones in, and adjacent to, the Okataina Volcanic Centre took place over time periods ranging from 60 to 220 ka (together with historical accounts of the 1886 AD Tarawera eruption). These indicate that neither dike intrusion nor caldera collapse have a measurable influence on fault displacement rates outside the volcanic complex. Within the volcanic complex, vertical displacement along the Whirinaki Fault zone increases by up to 50% between the caldera topographic margin and inner collapse boundary. This increase in vertical displacement is predominantly due to the collapse of the caldera 60 ka ago. In the Okataina Volcanic Centre, extension is accommodated by a combination of tectonic faulting, dike intrusion, and gravitational caldera collapse. Gravitational caldera collapse is however, superimposed on regional extension without contributing to it. Rift-orthogonal extension dominates across the Taupo Rift with a minor (</= 20 degrees) component of right-lateral slip increasing northwards. The regional principal horizontal extension direction rotates 30 degrees clockwise south to north along the rift. The modal principal horizontal extension direction for the Okataina Volcanic Centre trends ~145 degrees, approximately normal to northeast striking rift faults and intra-caldera linear vent zones, and oblique to north-south faults. Zones of crustal weakness, brittle deformation, and dilation at the intersections of northeast-southwest dip slip and north-south oblique slip active fault sets are inferred to locally promote the ascent of magma. Preliminary examination of volcanism outside the Okataina Volcanic Centre suggests that intersecting northeast-southwest and north-south fault sets may also play a role in defining the geometry of calderas and locations of volcanic centres throughout the Taupo Volcanic Zone. Outside these volcanic centres (e.g. Taupo and Okataina) active extension is primarily accommodated by normal faulting which is driven by tectonic processes (e.g. far-field plate motions) and is not attributed to dike intrusion. The Taupo Rift has not yet reached the stage where it is dominated by magma-assisted extension and is primarily a young tectonic rift in an arc environment.</p></p>

The Interrelationships between Faulting and Volcanism in the Okataina Volcanic Centre, New Zealand

<p>Continental rifts show close spatial relations between faulting and volcanism, however the interrelations between each process and their roles in the accommodation of regional extension are not well understood. The geometric and kinematic relations between an active silicic caldera complex and active faults in the upper 3-4 km of the crust (i.e. Taupo Rift) are investigated using regional gravity data, digital elevation models, outcrop mapping, seismic reflection lines, focal mechanisms and an historical account of the 1886 AD Tarawera eruption adjacent to, and within, the Okataina Volcanic Centre, New Zealand.The location and geometry of the Okataina Caldera were influenced by pre-existing faults. The caldera is elongate north-south, has a maximum subsidence of 3 +/- 0.5 km at the rift axis and occupies a 10 km hard-linked left step in the rift. The principal rift faults (55-75 degrees dip) define the location and geometry of the northwest and southeast margins and locally accommodate piecemeal caldera collapse. Segments of the east and west margins of the caldera margin are near vertical (70-90 degrees dip), trend north-south, and are inferred to be faults formed by the reactivation of a pervasive Mesozoic basement fabric (i.e. bedding, terrane boundaries, and/or faults). Measured displacements along the Paeroa and Whirinaki Fault zones in, and adjacent to, the Okataina Volcanic Centre took place over time periods ranging from 60 to 220 ka (together with historical accounts of the 1886 AD Tarawera eruption). These indicate that neither dike intrusion nor caldera collapse have a measurable influence on fault displacement rates outside the volcanic complex. Within the volcanic complex, vertical displacement along the Whirinaki Fault zone increases by up to 50% between the caldera topographic margin and inner collapse boundary. This increase in vertical displacement is predominantly due to the collapse of the caldera 60 ka ago. In the Okataina Volcanic Centre, extension is accommodated by a combination of tectonic faulting, dike intrusion, and gravitational caldera collapse. Gravitational caldera collapse is however, superimposed on regional extension without contributing to it. Rift-orthogonal extension dominates across the Taupo Rift with a minor (</= 20 degrees) component of right-lateral slip increasing northwards. The regional principal horizontal extension direction rotates 30 degrees clockwise south to north along the rift. The modal principal horizontal extension direction for the Okataina Volcanic Centre trends ~145 degrees, approximately normal to northeast striking rift faults and intra-caldera linear vent zones, and oblique to north-south faults. Zones of crustal weakness, brittle deformation, and dilation at the intersections of northeast-southwest dip slip and north-south oblique slip active fault sets are inferred to locally promote the ascent of magma. Preliminary examination of volcanism outside the Okataina Volcanic Centre suggests that intersecting northeast-southwest and north-south fault sets may also play a role in defining the geometry of calderas and locations of volcanic centres throughout the Taupo Volcanic Zone. Outside these volcanic centres (e.g. Taupo and Okataina) active extension is primarily accommodated by normal faulting which is driven by tectonic processes (e.g. far-field plate motions) and is not attributed to dike intrusion. The Taupo Rift has not yet reached the stage where it is dominated by magma-assisted extension and is primarily a young tectonic rift in an arc environment.</p></p>

Flank motion detected between 2010 and 2014 through InSAR time-series analysis at Pacaya Volcano, Guatemala

&lt;p&gt;Volcanic flank collapse has caused over 20,000 casualties in the past 400 years, and is one of the most dangerous hazards affecting communities and infrastructure near volcanoes. Flank instability has mostly been investigated at ocean volcanoes, due to their ability to trigger deadly tsunamis, however, these collapses are prevalent across volcanic settings, with all but one volcano in Guatemala with elevation over 2000m having experienced flank collapse, like Pacaya Volcano. At Pacaya, there is evidence for at least one past collapse, and transient SW flank motion has been identified accompanying vigorous eruptions in 2010 and 2014. We use InSAR time-series analysis to reveal, for the first time, long-term displacement of the SW flank of Pacaya during a period of volcanic quiescence from 2011-2013. This motion extended into 2014, with increased displacement rate attributed to dike intrusion during a major eruption. Subsequent static stress change analyses investigated the interactions between the modeled dike intrusion and detachment slip. Our research highlights that long-term flank motion might be more prevalent than currently recognized and that an awareness of existing structural weaknesses such as detachment faults and of possible magma-faulting interactions is vital when assessing the likelihood and style of volcanic flank collapse.&lt;/p&gt;

Dike Inflation Process Beneath Sakurajima Volcano, Japan, During the Earthquake Swarm of August 15, 2015

Magma intrusion usually causes seismicity and deformation in the surrounding rock and often leads to eruptions. A swarm of volcano-tectonic (VT) earthquakes associated with rapid dike intrusion in hours occurred beneath Sakurajima volcano on August 15, 2015. We determined the hypocenters and focal mechanisms of the VT earthquake swarm. The distributions of pressure (P)- and tension (T)-axes of the azimuths of the mechanisms are also obtained. The results indicate spatiotemporal changes of the distributions of the hypocenters and P- and T-axes. The hypocenters are distributed at depths of 0.3–1 km and 7:00–10:30 JST, and are located at depths of 0.3–3 km and 10:30–12:00 during which the seismic activity is the largest. At 12:00–24:00, the hypocenters are distributed in shallow and deep clusters at depths of 0.2–1 km and 1.5–3.5 km, respectively. The dike induced rapid ground deformation and is located between the shallow and deep clusters. The strike and opening directions of the dike are parallel to the NE–SW and NW–SE directions, respectively, corresponding to the regional maximum and minimum compression stress. The T-axes of the shallow cluster are distributed parallel to the opening direction of the dike. The P-axes of the deep cluster exhibit a pattern corresponding to the NE–SW direction and the T-axes are distributed in the NW–SE direction. In contrast, a 90° rotated pattern of strike-slip faulting is also observed at the deep cluster at 12:00–24:00, where the P-axes are distributed in the NW–SE direction and the T-axes are distributed in the NE–SW direction. This reflects the change in the stress field due to the dike inflation during the earthquake generation, and indicates that the alteration of stress in the vicinity of the dike due to the dike inflation and VT earthquakes are induced by the differential stress exceeding the brittle fracture strength of the rock. Future seismic and deformation observations in volcanoes will verify whether the spatiotemporal changes of the hypocenters and focal mechanism shown by this study are unique features of rapid dike intrusion.

An OBS Array to Investigate Offshore Seismicity during the 2018 Kīlauea Eruption

On 3 May 2018, Kīlauea Volcano, one of the most active volcanoes in the world, entered a new eruptive phase because of a dike intrusion in the East Rift zone. One day later, an Mw 6.9 earthquake, which was likely trigged by the dike intrusion, occurred in the submarine south flank of Kīlauea Volcano. In mid-July, an ocean-bottom seismometer (OBS) array consisting of 12 stations was deployed on the submarine south flank of Kīlauea Volcano to monitor the aftershocks and lava–water interaction near the ocean entry. Eleven OBSs were recovered in mid-September. Preliminary evaluation of the data reveals a large number of seismic and acoustic events, which provide a valuable dataset for understanding flank deformation and stability as well as lava–water interaction. Here, we introduce this dataset and document notable instrument malfunctions along with some initial seismic and acoustic observations.