About

Demian Saffer is a Professor and the Scott Petty Jr. Endowed Chair in the Department of Earth and Planetary Sciences at the University of Texas. His research interests include active tectonics, fault and sediment mechanics, and geohydrology. As the Director of the UT Institute for Geophysics, he contributes to understanding the Earth's dynamic processes, particularly focusing on fault systems and sediment behavior in tectonic settings. His work aims to elucidate the mechanics of faulting and sediment deformation, which are critical for understanding earthquake processes and subsurface fluid flow.

Research topics

• Geology
• Seismology
• Petrology
• Materials science
• Thermodynamics
• Physics
• Paleontology
• Biological system
• History
• Mechanics
• Composite material
• Geophysics
• Geochemistry
• Oceanography
• Biology

Selected publications

• Links between Low-T Dehydration and Recurring Shallow Slow Slip Events in the Northern Hikurangi Subduction Zone

  2026-03-14

  articleOpen access1st authorCorresponding

  In subduction zones, the depth-dependent release of fluids from compaction and metamorphic dehydration reactions in hydrous lithologies plays a key role in modulating pore fluid pressure, fault strength, and slip behavior along the megathrust. The depth-distribution of fluid release is also the primary control on volatile fluxes through the forearc, and on the residual volatile content of the subducting plate. Here, we investigate the inventory and release of fluids from altered oceanic crust by low-grade dehydration reactions (~50-350 °C) at the Northern Hikurangi subduction zone, where slip on the outer (shallow) megathrust is accommodated almost entirely in frequent, large shallow slow slip events (SSEs).Regional geophysical surveys and drilling during International Ocean Discovery Program (IODP) Expedition 375 show that the incoming plate of the Hikurangi Plateau carries a thick (>1.5 km) and extensively altered volcaniclastic sediment blanket characterized by an abundance of phyllosilicates (primarily Mg-smectite) and zeolite, and mineral-bound water contents as high as 14-16 wt.%, into the SSE source region. We quantify the distribution of fluid release from this sediment package by combining compaction trends to assess compactive water loss and thermodynamic phase equilibria models using sediment drill-core compositions to compute water release from dehydration reactions.We find that: (1) compactive dewatering dominates in the outermost 15-20 km of the forearc, where temperatures remain too low (

  PublisherDOI

• Comparative Boron Budgets of Subduction Zones and Implications for Volatile Cycling

  2026-03-14

  articleOpen access

  Boron is a key volatile tracer in subduction systems. It is concentrated in the pore waters of subducting sediments prior to diagenesis, partitions between aqueous and solid phases, is highly fluid-mobile, and is progressively released during devolitization. Exchangeable (aqueous + adsorbed) boron is primarily released by desorption at low temperatures (≤150 °C) and lattice bound boron is released by breakdown of hydrous phases at higher temperatures (

  PublisherDOI

• Slow Slip Accommodates the Full Plate Convergence Budget at the Northern Hikurangi Subduction Zone

  2026-03-13

  articleOpen access

  Accurately assessing strain accumulation and release in subduction zones is contingent upon robust detection and characterization of locking and slip along the megathrust. However, the distribution of slip on shallow, offshore plate boundaries is not well-resolved with onshore GNSS networks. At the Hikurangi Subduction Zone offshore Aotearoa-New Zealand, extensive investment has been made into seafloor geodetic techniques such as seafloor pressure and GNSS-acoustic, which have significantly improved observation and characterization of offshore SSEs. Despite their utility, oceanographic noise limits the ability of these seafloor techniques to detect SSEs. Formation pore pressure changes (as a proxy for volumetric strain) detected in borehole observatories have an enhanced signal-to-noise ratio and can reliably resolve deformation at the 10s of nanostrain-level, providing an improved view of shallow crustal deformation offshore.Here, we report on a suite of SSEs observed in two IODP borehole observatories in the northern Hikurangi Subduction Zone between 2018 and 2023 and model their slip distribution and magnitude. During this time, five SSEs were clearly recorded in the borehole pore pressure data. Four of these occurred spontaneously, and the borehole pressure changes correlate with surface displacement observed at onshore GNSS stations. In contrast, in early 2021, the Mw 7.2 East Cape earthquake triggered a near-trench SSE that was only captured by the observatories. We jointly invert changes in pore pressure with onshore GNSS displacements and seafloor pressure (when available) for slip distribution along a 2D transect for each of the events. Our inversions incorporate realistic elastic properties constrained by high-resolution seismic velocity models and logging-while-drilling data, which is crucial for accurately resolving slip distribution and magnitude. We find large differences in slip initiation and evolution characteristics during the 2021 triggered SSE compared to the spontaneous events. We also find that, in total, SSEs accommodate most (>80%) of the plate convergence budget along the shallow (

  PublisherDOI

• Tectonic shortening in the subduction trench and outer wedge, southern Hikurangi margin, New Zealand

  2026-03-14

  articleOpen accessSenior author

  Subduction zones generate the largest and most devastating earthquakes and tsunamis on Earth as a result of seismic slip on the megathrust fault. In addition to being capable of generating magnitude 8+ earthquakes, megathrusts also accommodate plate convergence via aseismic creep processes including episodic slow slip events. Above the megathrust, a portion of the overall plate convergence is accommodated as finite permanent strain (shortening) via slip along upper plate faults, tectonic folding, and reduction of sediment porosity (compaction). The most seaward expression of tectonic shortening in a subduction zone is focused within the outer accretionary wedge, but can also extend seaward of the main frontal thrust into sediments of the trench. Quantifying the strain budget among these different processes is essential for a better understanding of the partitioning between permanent inelastic strain and elastic strain accumulation as part of the seismic cycle – and thus ultimately toward an improved picture of subduction zone behavior and tsunami hazard. In this study, we use exceptionally detailed seismic reflection depth imaging and P-wave velocities to characterize sediment compaction within the outer wedge and trench along a profile of the southern Hikurangi subduction margin. Complementing these data with new constraints on stratigraphy, lithology and sediment physical properties, we provide the first quantifications of tectonic shortening attributable to sediment compaction on the Hikurangi margin. Our results demonstrate a broad region of compaction that extends more than 15 km seaward of the outermost faults. Future work beyond this study will explore relationships between pore scale compaction, proto-thrust development and active creep near the trench, in an attempt to provide a holistic understanding of strain accumulation in the outer wedge and trench.

  PublisherDOI

• Experimental constraints on the slip response of a slow-moving landslide to rainfall driven pore pressure changes

  2026-03-14

  articleOpen access

  Landslide motion spans a continuum from slow, steady creep to rapid catastrophic failure. However, the mechanisms controlling the timing, rate, and nature of sliding, the sensitivity of motion to perturbations driven by precipitation or human activity, and potential transitions from creep to catastrophic failure all remain poorly understood. The response of landslide basal shear zones to rainfall-driven changes in pore pressure and thus effective stress can be interpreted using rate and state friction, a framework that describes the constitutive behavior and sliding stability of frictional shear zones, and is widely applied to earthquake mechanics. Laboratory experiments provide direct constraints on these frictional properties, and thus hold the potential to illuminate the material properties and conditions that control basal slip. We investigate the frictional behavior of Oak Ridge earthflow, a slow-moving landslide in the Coast Ranges of central California hosted within a clay-rich mélange. We conduct a suite of direct shear experiments to characterize its frictional rheology, including both (1) the velocity dependence of friction measured from velocity step tests; and (2) frictional healing, or time-dependent restrengthening between slip events, measured via slide-hold-slide tests. Experiments are conducted across a range of normal stresses approximating the in-situ conditions of the active shear plane (0.3 – 2 MPa) and at sliding velocities that span the range of observed landslide creep (0.001 – 30 𝜇m/s).The shear plane material exhibits uniformly velocity strengthening behavior, characterized by a positive rate parameter (a-b), indicating that friction increases with increased slip rate, and is consistent with stable sliding. The values of (a-b) from laboratory experiments ranges from 0.001 – 0.015, in agreement with values inferred from coupled field observations of slide motion and pore pressure. Our results suggest that velocity strengthening friction, combined with modulation of effective stress through pore pressure, can generate slip transients, providing a direct mechanistic link between laboratory scale behavior and field observations of landslide motion.We also find that the clay rich materials entrained along the base of the slide exhibit little to no healing (𝛽 ≈ 0). Near zero healing implies that the slide does not restrengthen during extended periods of low water pressure during the dry California summer. In the absence of healing, slip velocity responds directly and immediately to changes in pore pressure, independent of the duration of dry periods. Taken together, velocity strengthening friction and little to no healing are consistent with the persistent creep observed in the field, where the slip rate is governed by the stress state, pore pressure, and rate dependence of friction. Notably, Oak Ridge earthflow has been active since at least the 1930’s (the date of first air photos). The laboratory derived frictional rheology provides a quantitative framework to explain the observed landslide slip response to changes in pore pressure and suggests that friction laws can be used not only to interpret past slide behavior, but potentially to predict landslide responses to future climate-driven hydrologic forcing or other external perturbations.

  PublisherDOI

• Not All Heterogeneity Is Equal: Length Scale of Frictional Property Variation as a Control on Subduction Megathrust Sliding Behavior

  Geophysical Research Letters · 2025-04-25 · 4 citations

  articleOpen access

  Abstract Heterogeneity in geometry, stress, and material properties is widely invoked to explain the observed spectrum of slow earthquake phenomena. However, the effects of length scale of heterogeneity on macroscopic fault sliding behavior remain underexplored. We investigate this question for subduction megathrusts, via linear stability analysis and quasi‐dynamic simulations of slip on a dipping fault characterized by rate‐and‐state friction. Frictional heterogeneity is imposed through alternating velocity‐strengthening and velocity‐weakening (VW) patches, over length scales spanning from those representative of basement relief (several km) to the entrainment of contrasting lithologies (100s of m). The resulting fault behavior is controlled by: (a) the average frictional properties of the fault, and (b) the size of VW blocks relative to a critical length scale. Reasonable ranges of these properties yield sliding behaviors spanning from stable sliding, to slow and seismic slip events that are confined within VW blocks or propagate along the entire fault.

  PublisherDOI

• Understanding the Physical Process of Unusually Long-duration Slow Slip Events: Insights from Stress Interaction and Environmental Influences in the Nankai Trough

  2025-03-14

  preprintOpen access

  JAMSTEC have been monitoring changes in underground fluid pressure, or "pore pressure," from boreholes near the site of the 1944 Tonankai earthquake in southwestern Japan. These changes are linked to Slow Slip Events (SSEs), which occur on the boundary between the Eurasian plate and the subducting Philippine Sea plate beneath the Nankai Trough. By connecting their borehole observatory (LTBMS) to a seafloor monitoring network (DONET), they now collect real-time pore pressure data, allowing them to update their SSE catalog.This updated catalog revealed something unusual: the SSE in February 2012 lasted significantly longer than similar events. Researchers studied pore pressure and seafloor pressure data to understand why. We found that the February SSE moved more slowly and lasted longer because of two key factors: internal and external forces.Internally, the SSE occurred in a region where little stress had built up on the fault, causing it to slip more slowly, consistent with frictional behavior on faults. Externally, we found that changes in seafloor pressure, driven by shifts in the Kuroshio Current (a major ocean current), coincided with the end of the February SSE. This suggests that the Kuroshio Current's meander may influence the duration of SSEs.Our study highlights that SSEs are not only shaped by fault interactions but also by environmental factors like ocean currents and atmospheric pressure. Understanding these influences is key to better predicting such events. These findings are based on a paper accepted by Tectonophysics (https://doi.org/10.1016/j.tecto.2024.230439), and we plans to share additional insights and recent practical analysis in our presentation.

  PublisherDOI

• The Roles of Shear Displacement and Normal Stress on Earthquake Nucleation in Meter‐Scale Laboratory Faults

  Journal of Geophysical Research Solid Earth · 2025-08-01 · 1 citations

  articleOpen access

  Abstract Earthquake nucleation is a fundamental problem in earthquake science and has practical implications for forecasting seismic hazards. Laboratory experiments performed on large, meter‐scale fault systems offer unique insights into the nucleation process because the migration and expansion of the nucleation zone can be precisely detected, measured, and characterized using arrays of local strain and slip measurements. We report on a series of laboratory experiments conducted on a 1‐m direct shear machine. We sheared layers of quartz gouge between roughened acrylic forcing blocks over a range of normal stresses between 3 and 12 MPa, generating a spectrum of slip modes, ranging from aseismic creep to fast‐dynamic rupture. Co‐seismic slip, peak slip velocity, and high‐frequency acoustic energy content of laboratory earthquakes increases systematically with both cumulative fault slip and normal stress. Slower and smaller laboratory earthquake sequences have larger nucleation zones, creep more during their inter‐seismic period, and are deficient in high‐frequency energy compared to larger and faster rupture sequences. We find that the critical nucleation length scale, H* , scales inversely with cumulative fault slip and normal stress. A reduction in H* and an increase in event size can be explained by a decrease in the critical slip distance, D c , or an increase in the frictional rate parameter b – a and is likely driven by shear localization. Together, our results indicate that homogeneous, mature fault zones that have undergone more cumulative fault slip are expected to have smaller H* and can more easily host dynamic instabilities, relative to immature faults.

  PublisherOA PDFDOI

• Migrating shallow slow slip on the Nankai Trough megathrust captured by borehole observatories

  Science · 2025-06-26 · 9 citations

  articleCorresponding

  Patterns of strain accumulation and release offshore in subduction zones are directly linked to the potential for shallow coseismic slip and tsunamigenesis, but these patterns remain elusive. In this work, we analyze formation pore pressure records from three offshore borehole observatories at the Nankai subduction zone, Honshu, Japan, to capture detailed slip-time histories of two slow slip events (SSEs) along the outermost reaches of the plate boundary. Slip initiates ~30 kilometers landward of the trench; migrates seaward at 1 to 2 kilometers per day to within a few kilometers of, and possibly breaching, the trench; and coincides with the onset and migration of tremor and/or very-low-frequency earthquakes. The SSE source region lies in a zone of high pore fluid pressure and low stress, which provides clear observational evidence linking these factors to shallow slow earthquakes.

  PublisherDOI

• Effects of incoming polygonal fault systems on subduction zone and slow slip behavior

  Science Advances · 2025-07-04

  articleOpen access

  The physical properties of subduction inputs profoundly influence megathrust slip behavior. Seismic data reveal extensive polygonal fault systems (PFSs) in the input sequences of the Hikurangi Margin and Nankai Trough. The mechanical and hydrological effects of these incoming PFSs on subduction zones are potentially substantial. Here, we investigate their effects following transport into the accretionary wedge by integrating discrete-element modeling with three-dimensional seismic interpretation. We find that the typical dips of the incoming PFSs overlap with modeled dips prone to reactivation and confirm that subducting PFSs can be reactivated and gradually evolve into major thrust faults. Comparisons with electromagnetic data indicate that PFSs may provide conduits for fluid leakage along the plate interface, coincide with disrupted strata and decreased shear stress, and enhance geometric and stress heterogeneity along the megathrust. These suggest that PFSs may play a previously unrecognized role in contributing to shallow slow earthquake phenomena in subduction zones.

  PublisherDOI

Recent grants

• Collaborative Research: Laboratory Study of the Mechanics and Physical Properties of the Active San Andreas Fault Zone From Phase III SAFOD Cores

  NSF · $284k · 2008–2010

• Collaborative Research: Laboratory Investigations of Fault Zone Mechanical Behavior and Fluid Overpressure (EOR for IODP NanTroSEIZE Expeditions 314, 315, and 316)

  NSF · $99k · 2008–2011

• Subseafloor Observatory Science in the Nankai Trough: Analysis of Earthquakes and Hydraulic Transients, and Installation of a Community Borehole Facility

  NSF · $83k · 2013–2015

• Collaborative Research: Physical properties of the Alpine Fault, New Zealand: Mechanical and hydrological processes in the brittle fault core and surrounding damage zone

  NSF · $316k · 2012–2016

• Collaborative Research: Controls on along-strike variations in locked and creeping megathrust behavior at the Hikurangi convergent margin

  NSF · $370k · 2016–2020

Frequent coauthors

• Laura Wallace

  132 shared

• Sean Toczko

  122 shared

• Harold Tobin

  Earth and Space Research

  120 shared

• Hiroko Kitajima

  114 shared

• Michael B. Underwood

  102 shared

• Matt J. Ikari

  University of Bremen

  101 shared

• Gregory F. Moore

  99 shared

• Chris Marone

  Sapienza University of Rome

  94 shared

Awards & honors

• AGU Fellow