Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone

International audienceFault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging‐wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP‐2). We present observational evidence for extensive fracturing and high hanging‐wall hydraulic conductivity (∼10−9 to 10−7 m/s, corresponding to permeability of ∼10−16 to 10−14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP‐2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging‐wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off‐fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation

Bedrock geology of DFDP-2B, central Alpine Fault, New Zealand

<p>During the second phase of the Alpine Fault, Deep Fault Drilling Project (DFDP) in the Whataroa River, South Westland, New Zealand, bedrock was encountered in the DFDP-2B borehole from 238.5–893.2 m Measured Depth (MD). Continuous sampling and meso- to microscale characterisation of whole rock cuttings established that, in sequence, the borehole sampled amphibolite facies, Torlesse Composite Terrane-derived schists, protomylonites and mylonites, terminating 200–400 m above an Alpine Fault Principal Slip Zone (PSZ) with a maximum dip of 62°. The most diagnostic structural features of increasing PSZ proximity were the occurrence of shear bands and reduction in mean quartz grain sizes. A change in composition to greater mica:quartz + feldspar, most markedly below c. 700 m MD, is inferred to result from either heterogeneous sampling or a change in lithology related to alteration. Major oxide variations suggest the fault-proximal Alpine Fault alteration zone, as previously defined in DFDP-1 core, was not sampled.</p

Convalescent plasma in patients admitted to hospital with COVID-19 (RECOVERY): a randomised controlled, open-label, platform trial

SummaryBackground Azithromycin has been proposed as a treatment for COVID-19 on the basis of its immunomodulatoryactions. We aimed to evaluate the safety and efficacy of azithromycin in patients admitted to hospital with COVID-19.Methods In this randomised, controlled, open-label, adaptive platform trial (Randomised Evaluation of COVID-19Therapy [RECOVERY]), several possible treatments were compared with usual care in patients admitted to hospitalwith COVID-19 in the UK. The trial is underway at 176 hospitals in the UK. Eligible and consenting patients wererandomly allocated to either usual standard of care alone or usual standard of care plus azithromycin 500 mg once perday by mouth or intravenously for 10 days or until discharge (or allocation to one of the other RECOVERY treatmentgroups). Patients were assigned via web-based simple (unstratified) randomisation with allocation concealment andwere twice as likely to be randomly assigned to usual care than to any of the active treatment groups. Participants andlocal study staff were not masked to the allocated treatment, but all others involved in the trial were masked to theoutcome data during the trial. The primary outcome was 28-day all-cause mortality, assessed in the intention-to-treatpopulation. The trial is registered with ISRCTN, 50189673, and ClinicalTrials.gov, NCT04381936.Findings Between April 7 and Nov 27, 2020, of 16 442 patients enrolled in the RECOVERY trial, 9433 (57%) wereeligible and 7763 were included in the assessment of azithromycin. The mean age of these study participants was65·3 years (SD 15·7) and approximately a third were women (2944 [38%] of 7763). 2582 patients were randomlyallocated to receive azithromycin and 5181 patients were randomly allocated to usual care alone. Overall,561 (22%) patients allocated to azithromycin and 1162 (22%) patients allocated to usual care died within 28 days(rate ratio 0·97, 95% CI 0·87–1·07; p=0·50). No significant difference was seen in duration of hospital stay (median10 days [IQR 5 to >28] vs 11 days [5 to >28]) or the proportion of patients discharged from hospital alive within 28 days(rate ratio 1·04, 95% CI 0·98–1·10; p=0·19). Among those not on invasive mechanical ventilation at baseline, nosignificant difference was seen in the proportion meeting the composite endpoint of invasive mechanical ventilationor death (risk ratio 0·95, 95% CI 0·87–1·03; p=0·24).Interpretation In patients admitted to hospital with COVID-19, azithromycin did not improve survival or otherprespecified clinical outcomes. Azithromycin use in patients admitted to hospital with COVID-19 should be restrictedto patients in whom there is a clear antimicrobial indication

Parametric Testing of EQTransformer’s Performance against a High-Quality, Manually Picked Catalog for Reliable and Accurate Seismic Phase Picking

This study evaluates EQTransformer, a deep learning model, for earthquake detection and phase picking using seismic data from the Southern Alps, New Zealand. Using a robust, independent dataset containing more than 85,000 manual picks from 13 stations spanning almost nine years, we assess EQTransformer’s performance and limitations in a practical application scenario. We investigate key parameters such as overlap and probability threshold and their influences on detection consistency and false positives, respectively. EQTransformer’s probability outputs show a limited correlation with pick accuracy, emphasizing the need for careful interpretation. Our analysis of illustrative signals from three seismic networks highlights challenges of consistently picking first arrivals when reflected or refracted phases are present. We find that an overlap length of 55 s balances detection consistency and computational efficiency, and that a probability threshold of 0.1 balances detection rate and false positives. Our study thus offers insights into EQTransformer’s capabilities and limitations, highlighting the importance of parameter selection for optimal results

Illuminating the Pre-, Co-, and Post-Seismic Phases of the 2016 M7.8 Kaikōura Earthquake With 10 Years of Seismicity

The 2016 M7.8 Kaikōura earthquake is one of the most complex earthquakes in recorded history, with significant rupture of at least 21 crustal faults. Using a matched-filter detection routine, precise cross-correlation pick corrections, and accurate location and relocation techniques, we construct a catalog of 33,328 earthquakes between 2009 and 2020 on and adjacent to the faults that ruptured in the Kaikōura earthquake. We also compute focal mechanisms for 1,755 of the earthquakes used as templates. Using this catalog we reassess the rupture pathway of the Kaikōura earthquake. In particular we show that: (a) the earthquake nucleated on the Humps Fault; (b) there is a likely linking offshore reverse fault between the southern fault system and the Papatea Fault, which could explain the anomalously high slip on the Papatea Fault; (c) the faults that ruptured in the 2013 Cook Strait sequence were reactivated by the Kaikōura earthquake and may have played a role in the termination of the earthquake; and (d) no seismicity on an underlying subduction interface is observed beneath almost all of the ruptured region suggesting that if deformation did occur on the plate interface then it occurred aseismically and did not play a significant role in generating co-seismic ground motion.ISSN:2169-9313ISSN:0148-0227ISSN:2169-935

Variations in Seismogenic Thickness Along the Central Alpine Fault, New Zealand, Revealed by a Decade's Relocated Microseismicity

©2018. American Geophysical Union. All Rights Reserved. The Alpine Fault is an oblique strike-slip fault that is known to fail in large magnitude (M7–8) earthquakes, yet it is currently seismically quiescent. We examine the low-magnitude earthquake activity occurring along the central portion of the Alpine Fault using seismic data from five temporary seismic networks deployed for various lengths of time between late 2008 and early 2017. Starting from continuous seismic data, we detect earthquake arrivals and construct the longest and most extensive microearthquake catalog for the central Alpine Fault region to date, containing 9,111 earthquakes. This enables us to study the distribution and characteristics of the seismicity in unprecedented detail. Earthquake locations are constrained by high-quality automatic and manual picks, and we perform relocations using waveform cross-correlation to better constrain hypocenters. We have derived a new local magnitude scale calibrated by M w values. Magnitudes range between M L −1.2 and 4.6, and our catalog is complete above M L 1.1. Earthquakes mainly occur southeast of the Alpine Fault (in the hanging wall) and exhibit low magnitudes. We observe a lack of seismicity beneath Aoraki/Mount Cook, which we associate with high uplift rates and high heat flow. Seismogenic cutoff depths vary along the strike of the Alpine Fault from 8 km, beneath the highest topography, to 20 km in the adjacent areas

Volcanic Unrest at Taupō Volcano in 2019: Causes, Mechanisms and Implications

Taupō volcano, New Zealand, is a large caldera volcano that has been highly active through the Holocene. It most recently erupted ∼1,800 years ago but there have been multiple periods of historic volcanic unrest. We use seismological and geodetic analysis to show that in 2019 Taupō underwent a period of unrest characterized by increased seismic activity through multiple swarms and was accompanied by ground deformation within the caldera. The earthquakes, which include non-double-couple events, serve to outline an aseismic zone beneath the most recent eruptive vents. This aseismic zone is coincident with an inflating source, based on forward modeling of ground deformation data. We infer that this aseismic and deforming region delineates the location of the present day magma reservoir that is ≥250 km3 in volume and has a melt fraction of >20%–30%, inhibiting seismic activity. Our analysis shows that the 2019 unrest at Taupō was volcanic in nature and origin, demonstrating that this is an active and potentially hazardous volcano, and that improving our monitoring and understanding of its behavior is important

Bedrock geology of DFDP-2B, central Alpine Fault, New Zealand

During the second phase of the Alpine Fault, Deep Fault Drilling Project (DFDP) in the Whataroa River, South Westland, New Zealand, bedrock was encountered in the DFDP-2B borehole from 238.5–893.2 m Measured Depth (MD). Continuous sampling and meso- to microscale characterisation of whole rock cuttings established that, in sequence, the borehole sampled amphibolite facies, Torlesse Composite Terrane-derived schists, protomylonites and mylonites, terminating 200–400 m above an Alpine Fault Principal Slip Zone (PSZ) with a maximum dip of 62°. The most diagnostic structural features of increasing PSZ proximity were the occurrence of shear bands and reduction in mean quartz grain sizes. A change in composition to greater mica:quartz + feldspar, most markedly below c. 700 m MD, is inferred to result from either heterogeneous sampling or a change in lithology related to alteration. Major oxide variations suggest the fault-proximal Alpine Fault alteration zone, as previously defined in DFDP-1 core, was not sampled