Repeating caldera collapse events constrain fault friction at the kilometer scale.

Fault friction is central to understanding earthquakes, yet laboratory rock mechanics experiments are restricted to, at most, meter scale. Questions thus remain as to the applicability of measured frictional properties to faulting in situ. In particular, the slip-weakening distance [Formula: see text] strongly influences precursory slip during earthquake nucleation, but scales with fault roughness and is challenging to extrapolate to nature. The 2018 eruption of K̄ilauea volcano, Hawaii, caused 62 repeatable collapse events in which the summit caldera dropped several meters, accompanied by [Formula: see text] 4.7 to 5.4 very long period (VLP) earthquakes. Collapses were exceptionally well recorded by global positioning system (GPS) and tilt instruments and represent unique natural kilometer-scale friction experiments. We model a piston collapsing into a magma reservoir. Pressure at the piston base and shear stress on its margin, governed by rate and state friction, balance its weight. Downward motion of the piston compresses the underlying magma, driving flow to the eruption. Monte Carlo estimation of unknowns validates laboratory friction parameters at the kilometer scale, including the magnitude of steady-state velocity weakening. The absence of accelerating precollapse deformation constrains [Formula: see text] to be [Formula: see text] mm, potentially much less. These results support the use of laboratory friction laws and parameters for modeling earthquakes. We identify initial conditions and material and magma-system parameters that lead to episodic caldera collapse, revealing that small differences in eruptive vent elevation can lead to major differences in eruption volume and duration. Most historical basaltic caldera collapses were, at least partly, episodic, implying that the conditions for stick-slip derived here are commonly met in nature.

Magma reservoir failure and the onset of caldera collapse at Kilauea Volcano in 2018.

Caldera-forming eruptions are among Earth's most hazardous natural phenomena, yet the architecture of subcaldera magma reservoirs and the conditions that trigger collapse are poorly understood. Observations from the formation of a 0.8-cubic kilometer basaltic caldera at Kilauea Volcano in 2018 included the draining of an active lava lake, which provided a window into pressure decrease in the reservoir. We show that failure began after <4% of magma was withdrawn from a shallow reservoir beneath the volcano's summit, reducing its internal pressure by ~17 megapascals. Several cubic kilometers of magma were stored in the reservoir, and only a fraction was withdrawn before the end of the eruption. Thus, caldera formation may begin after withdrawal of only small amounts of magma and may end before source reservoirs are completely evacuated.

Magma chambers: what we can, and cannot, learn from volcano geodesy.

Geodetic observations on volcanoes can reveal important aspects of crustal magma chambers. The rate of decay of deformation with distance reflects the centroid depth of the chamber. The amplitude of the deformation is proportional to the product of the pressure change and volume of the reservoir. The ratio of horizontal to vertical displacement is sensitive to chamber shape: sills are efficient at generating vertical displacement, while stocks produce more horizontal deformation. Geodesy alone cannot constrain important parameters such as chamber volume or pressure; furthermore, kinematic models have no predictive power. Elastic response combined with influx proportional to pressure gradient predicts an exponentially decaying flux, leading to saw-tooth inflation cycles observed at some volcanoes. Yet many magmatic systems exhibit more complex temporal behaviour. Wall rock adjacent to magma reservoirs cannot behave fully elastically. Modern conceptual models of magma chambers also include cumulate and/or mush zones, with potentially multi-level melt lenses. A viscoelastic shell surrounding a spherical magma chamber significantly modifies the predicted time-dependent response; post-eruptive inflation can occur without recharge if the magma is sufficiently incompressible relative to the surrounding crust (Segall P. 2016 J. Geophys. Res. Solid Earth, 121, 8501-8522). Numerical calculations confirm this behaviour for both oblate and prolate ellipsoidal chambers surrounded by viscoelastic aureoles. Interestingly, the response to a nearly instantaneous pressure drop during an explosive eruption can be non-monotonic as the rock around the chamber relaxes at different rates. Pressure-dependent recharge of a non-Newtonian magma in an elastic crust leads to an initially high rate of inflation which slows over time; behaviour that has been observed in some magmatic systems. I close by discussing future challenges in volcano geodesy. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.

Stress control of deep rift intrusion at Mauna Loa volcano, Hawaii.

Mauna Loa volcano, Hawaii, deforms by a combination of shallow dike intrusions in the rift zones and earthquakes along the base of the volcano, but it is not known how the spreading is accommodated in the lower part of the volcanic edifice. We present evidence from interferometric synthetic aperture radar data for secular inflation of a dike-like magma body at intermediate depth in the southwest rift zone during 2002 to 2005. Magma accumulation occurred in a section of the rift zone that was unclamped by previous dikes and earthquakes, suggesting that stress transfer plays an important role in controlling subsurface magma accumulation.

Earthquakes triggered by silent slip events on Kilauea volcano, Hawaii.

Slow-slip events, or 'silent earthquakes', have recently been discovered in a number of subduction zones including the Nankai trough in Japan, Cascadia, and Guerrero in Mexico, but the depths of these events have been difficult to determine from surface deformation measurements. Although it is assumed that these silent earthquakes are located along the plate megathrust, this has not been proved. Slow slip in some subduction zones is associated with non-volcanic tremor, but tremor is difficult to locate and may be distributed over a broad depth range. Except for some events on the San Andreas fault, slow-slip events have not yet been associated with high-frequency earthquakes, which are easily located. Here we report on swarms of high-frequency earthquakes that accompany otherwise silent slips on Kilauea volcano, Hawaii. For the most energetic event, in January 2005, the slow slip began before the increase in seismicity. The temporal evolution of earthquakes is well explained by increased stressing caused by slow slip, implying that the earthquakes are triggered. The earthquakes, located at depths of 7-8 km, constrain the slow slip to be at comparable depths, because they must fall in zones of positive Coulomb stress change. Triggered earthquakes accompanying slow-slip events elsewhere might go undetected if background seismicity rates are low. Detection of such events would help constrain the depth of slow slip, and could lead to a method for quantifying the increased hazard during slow-slip events, because triggered events have the potential to grow into destructive earthquakes.

Post-earthquake ground movements correlated to pore-pressure transients.

Large earthquakes alter the stress in the surrounding crust, leading to triggered earthquakes and aftershocks. A number of time-dependent processes, including afterslip, pore-fluid flow and viscous relaxation of the lower crust and upper mantle, further modify the stress and pore pressure near the fault, and hence the tendency for triggered earthquakes. It has proved difficult, however, to distinguish between these processes on the basis of direct field observations, despite considerable effort. Here we present a unique combination of measurements consisting of satellite radar interferograms and water-level changes in geothermal wells following two magnitude-6.5 earthquakes in the south Iceland seismic zone. The deformation recorded in the interferograms cannot be explained by either afterslip or visco-elastic relaxation, but is consistent with rebound of a porous elastic material in the first 1-2 months following the earthquakes. This interpretation is confirmed by direct measurements which show rapid (1-2-month) recovery of the earthquake-induced water-level changes. In contrast, the duration of the aftershock sequence is projected to be approximately 3.5 years, suggesting that pore-fluid flow does not control aftershock duration. But because the surface strains are dominated by pore-pressure changes in the shallow crust, we cannot rule out a longer pore-pressure transient at the depth of the aftershocks. The aftershock duration is consistent with models of seismicity rate variations based on rate- and state-dependent friction laws.

Resuscitating hypothermic dogs after 2 hours of circulatory arrest below 6 degrees C.

BACKGROUND: Ultraprofound hypothermia may have a place in trauma rescue and resuscitation. We describe resuscitation of dogs after asanguineous perfusion and circulatory arrest of 2 hours at 2 degrees to 4 degrees C. METHODS: Nine dogs were cooled using a bypass apparatus and their circulating blood replaced with bicarbonated Hextend (Abbott, North Chicago, IL). Perfusion was continued to 2 degrees to 4 degrees C, and 60 mL of 2 mol/L KCl and 20 mL of 50% MgSO(4).7H(2)O were infused intra-arterially, and circulation was arrested for 2 hours. The dogs were then rewarmed, transfused, defibrillated, weaned from bypass, and allowed to awaken. Preoperative and postoperative biochemistry and hematology were compared. RESULTS: Six dogs recovered fully. One of these dogs died of an infection 2 weeks later. Three other dogs never recovered because of technical or procedural difficulties. Biochemical and hematologic parameters were normal by 3 weeks. CONCLUSION: Hypothermic blood substitution with Hextend allows resuscitation after 2 hours of ice-cold circulatory arrest in dogs.

Testing time-predictable earthquake recurrence by direct measurement of strain accumulation and release.

Probabilistic estimates of earthquake hazard use various models for the temporal distribution of earthquakes, including the 'time-predictable' recurrence model formulated by Shimazaki and Nakata (which incorporates the concept of elastic rebound described as early as 1910 by H. F. Reid). This model states that an earthquake occurs when the fault recovers the stress relieved in the most recent earthquake. Unlike time-independent models (for example, Poisson probability), the time-predictable model is thought to encompass some of the physics behind the earthquake cycle, in that earthquake probability increases with time. The time-predictable model is therefore often preferred when adequate data are available, and it is incorporated in hazard predictions for many earthquake-prone regions, including northern California, southern California, New Zealand and Japan. Here we show that the model fails in what should be an ideal locale for its application -- Parkfield, California. We estimate rigorous bounds on the predicted recurrence time of the magnitude approximately 6 1966 Parkfield earthquake through inversion of geodetic measurements and we show that, according to the time-predictable model, another earthquake should have occurred by 1987. The model's poor performance in a relatively simple tectonic setting does not bode well for its successful application to the many areas of the world characterized by complex fault interactions.

Sudden aseismic fault slip on the south flank of Kilauea volcano.

One of the greatest hazards associated with oceanic volcanoes is not volcanic in nature, but lies with the potential for catastrophic flank failure. Such flank failure can result in devastating tsunamis and threaten not only the immediate vicinity, but coastal cities along the entire rim of an ocean basin. Kilauea volcano on the island of Hawaii, USA, is a potential source of such flank failures and has therefore been monitored by a network of continuously recording geodetic instruments, including global positioning system (GPS) receivers, tilt meters and strain meters. Here we report that, in early November 2000, this network recorded transient southeastward displacements, which we interpret as an episode of aseismic fault slip. The duration of the event was about 36 hours, it had an equivalent moment magnitude of 5.7 and a maximum slip velocity of about 6[?]cm per day. Inversion of the GPS data reveals a shallow-dipping thrust fault at a depth of 4.5[?]km that we interpret as the down-dip extension of the Hilina Pali--Holei Pali normal fault system. This demonstrates that continuously recording geodetic networks can detect accelerating slip, potentially leading to warnings of volcanic flank collapse.