This dataset contains lake levelling measurements from Lake Taupō covering the period 1979-2021. If you use this data please cite: Otway, P., Illsley-Kemp, F., Mestel, E.R.H. Review of lake levelling surveys at Lake Taupō, 1979-2021. New Zealand Journal of Geology and Geophysics, 2021.
Abstract Unusually deep earthquakes occur beneath rift segments with and without surface expressions of magmatism in the East African Rift system. The Tanganyika rift is part of the Western rift and has no surface evidence of magmatism. The TANG14 array was deployed in the southern Tanganyika rift, where earthquakes of magnitude up to 7.4 have occurred, to probe crust and upper mantle structure and evaluate fault kinematics. Four hundred seventy‐four earthquakes detected between June 2014 and September 2015 are located using a new regional velocity model. The precise locations, magnitudes, and source mechanisms of local and teleseismic earthquakes are used to determine seismogenic layer thickness, delineate active faults, evaluate regional extension direction, and evaluate kinematics of border faults. The active faults span more than 350 km with deep normal faults transecting the thick Bangweulu craton, indicating a wide plate boundary zone. The seismogenic layer thickness is 42 km, spanning the entire crust beneath the rift basins and their uplifted flanks. Earthquakes in the upper mantle are also detected. Deep earthquakes with steep nodal planes occur along subsurface projections of Tanganyika and Rukwa border faults, indicating that large offset (≥5 km) faults penetrate to the base of the crust, and are the current locus of strain. The focal mechanisms, continuous depth distribution, and correlation with mapped structures indicate that steep, deep border faults maintain a half‐graben morphology over at least 12 Myr of basin evolution. Fault scaling based on our results suggests that M > 7 earthquakes along Tanganyika border faults are possible.
<p>Taup&#333; volcano, in the centre of North Island, Aotearoa New Zealand, is a frequently active rhyolitic caldera volcano that was the site of Earth&#8217;s most recent supereruption (Oruanui ~25 ka)<sup>1,2</sup>. It has erupted 28 times since then, and continues to display signs of unrest (seismicity and surface deformation), with periods of elevated unrest on roughly decadal timescales<sup>3</sup>. Any resumption of eruptive activity at the volcano poses a major source of hazard, and interactions between the magma reservoir and the regional tectonics that lead to unrest and possible eruption are not well understood. The location of the modern magma reservoir has been previously constrained by study of past eruptive products and some geophysical imaging (gravity, broad-scale tomography)<sup>2</sup>. Earthquake patterns during a 2019 unrest episode have also been used to infer the location and size (>~250 km<sup>3</sup>) of the modern-day reservoir<sup>4</sup>, but its location and extent have not yet been directly imaged. As part of the interdisciplinary ECLIPSE project, seismological methods are being used to investigate the Taup&#333; reservoir, combining data from the national GeoNet seismic network with records from a temporary 13 broadband seismometer network. Development of the ECLIPSE network approximately doubles the number of seismic stations within 10 km of the lake shore.</p><p>We present here initial results on the characterisation of the seismicity in the Taup&#333; region. These results include the improvement of earthquake locations with the addition of picks from the ECLIPSE stations and the use of automated machine learning phase picking and association techniques. We also present initial results from the cross correlation of ambient noise between stations in the ECLIPSE network for the use in ambient noise surface wave tomography, with many of the station pairs crossing the region most likely to contain the modern-day magma reservoir.</p><p><sup>1</sup> Wilson CJN J. Volcanol Geotherm Res 112, 133 (2001) <br><sup>2</sup> Barker SJ et al. NZ J Geol Geophys 64, 320 (2021) <br><sup>3</sup> Potter SH et al. Bull Volcanol 77, 78 (2015) <br><sup>4</sup> Illsley&#8208;Kemp F et al. G-cubed 22, e2021GC009803 (2021)</p>
Abstract Volcanic tremor is a crucial indicator for assessing the state and hazard potential of volcanic systems. At Whakaari (White Island volcano, Aotearoa New Zealand), a pulsed tremor signal emerged after a hydrothermal explosion in August 2012. The tremor accompanied the extrusion of a lava dome, before gradually disappearing prior to the onset of renewed hydrothermal activity in January 2013. We interpret this seismic signal to represent discrete gas transfers from a magmatic intrusion toward a permeable cap—possibly a hydrothermal seal—in the upper layers of Whakaari's hydrothermal system. Such tremor may thus be associated with heightened potential for hazardous explosive activity but is difficult to detect using conventional seismic monitoring parameters. To highlight the emergence of subtle periodic signals, we experiment with Lomb‐Scargle periodograms (LS). LS detect the tremor 5 days before it becomes visible in seismograms, thus facilitating the recognition of such elusive seismic patterns.
The datasets provided here are the seismic anisotropy results for the four seperate regions of New Zealand, reported and discussed in Illsley-Kemp et al., Geochemistry, Geophysics, Geosystems, 2019 (10.1029/2019GC008529). If you use this date, please cite the following paper: Illsley-Kemp, F., Savage, M. K., Wilson, C. J. N., & Bannister, S., 2019, 10.1029/2019GC008529. Mapping Stress and Structure from Subducting Slab to Magmatic Rift: Crustal Seismic Anisotropy of the North Island, New Zealand. Geochemistry, Geophysics, Geosystems. The data are csv files in the same format as MFAST output (http://mfast-package.geo.vuw.ac.nz), with each column corresponding to the following: 1: Result ID 2: Station code 3: Station latitude 4: Station longitude 5: Earthquake ID (after GeoNet) 6: Year 7: Julian day on which the event occurred, with decimal digits giving the fraction of the day 8: Earthquake latitude 9: Earthquake longitude 10: Earthquake-station distance (km) 11: Earthquake depth (km) 12: Earthquake magnitude 13: Back azimuthal angle 14: Initial polarisation of the shear wave in degrees 15: Error of Spol in degrees, one standard deviation 16: Start time of the selected measurement window in seconds, relative to the start of the seismogram at t = 0 17: End time of the selected measurement window in seconds, relative to the start of the seismogram at t = 0 18: Not used 19: Not used 20: Signal to noise ratio 21: Delay time (δt) between fast and slow shear wave in seconds 22: Error of δt in degrees, one standard deviation 23: Angle of the orientation of the fast shear wave (φ), in degrees from North 24: Error of φ in degrees, one standard deviation 25: Angle of incidence at the station, measured against a horizontal plane in degrees, where 0 means vertical incidence 26: Not used 27: Type of measurement. This field contains the measurement code that is used, the number of measurement window start times and the number of window end times 28: Not used 29: Not used 30: Nyquist frequency of the event in Hz 31: Evaluation of the measurement quality 32: Lower corner frequency of the bandpass filter in Hz 33: Higher corner frequency of the bandpass filter in Hz 34: Angle between the initial polarisation and the fast orientation in degrees 35: Not used 36: Not used 37: The maximum value of the eigenvalue of the corrected covariance matrix 38: The number of degrees of freedom in the measurement 39: The minimum value of the eigenvalue of the covariance matrix before it was scaled to have the 95% confidence level set to 1 40: The S-wave travel time between the earthquake and the station 41: The dominant frequency in the S wave, determined from the frequency at the maximum spectral amplitude
Theory and geoscientific observations demonstrate that plate stretching, heating, faulting, active and frozen magma intrusions, and extrusive eruptive products are consequences of mantle upwelling mechanism driving continental rifting. Problematic to this picture is the lack of consensus on how, when and where these processes modify the crust’s thermal and mechanical structure. We use data from East Africa’s 300-km wide Turkana Depression to investigate how the superposition of these rift processes and the spatial migration of the active plate boundary through time within one geodynamic setting modify the crust’s structure. Utilizing ambient noise seismic methods and data from the 34 station Turkana Rift Arrays Investigating Lithospheric Structure (TRAILS) seismic network, we invert for Rayleigh and Love tomographic models and overlay results with our local earthquakes crustal splitting results. Preliminary results show that regions that experienced Eocene flood magmatism have localized high Vs of > 3.4 km/s at mid-lower crustal depths implying that flood magmatism is fed by unknown localized centers and/or dike swarms. Quaternary eruptive centers with Vs < 3.4 km/s at mid-lower crustal depths are punctuated and irregularly spaced suggesting that bottom-up mantle upwelling influence their location. Regions with superposed Cretaceous-Paleogene and Miocene-Recent rift phases have persistent low velocities (Vs ≥ 3.8 km/s) to the mid-crust with thinner crust (~ 20 km); the active Miocene-Recent rift structures are oblique to the largely inactive Cretaceous-Paleogene rift structures implying no reactivation of pre-existing structures during modern-day rifting.
Abstract Transform faults are a fundamental tenet of plate tectonics, connecting offset extensional segments of mid‐ocean ridges in ocean basins worldwide. The current consensus is that oceanic transform faults initiate after the onset of seafloor spreading. However, this inference has been difficult to test given the lack of direct observations of transform fault formation. Here we integrate evidence from surface faults, geodetic measurements, local seismicity, and numerical modeling of the subaerial Afar continental rift and show that a proto‐transform fault is initiating during the final stages of continental breakup. This is the first direct observation of proto‐transform fault initiation in a continental rift and sheds unprecedented light on their formation mechanisms. We demonstrate that they can initiate during late‐stage continental rifting, earlier in the rifting cycle than previously thought. Future studies of volcanic rifted margins cannot assume that oceanic transform faults initiated after the onset of seafloor spreading.
This dataset contains lake levelling measurements from Lake Taupō covering the period 1979-2021. If you use this data please cite: Otway, P., Illsley-Kemp, F., Mestel, E.R.H. Review of lake levelling surveys at Lake Taupō, 1979-2021. New Zealand Journal of Geology and Geophysics, 2021.
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