About

Melodie French is an Associate Professor in the Department of Earth, Environmental and Planetary Sciences at Rice University. Her research focuses on studying the mechanical properties of rocks through high pressure and temperature experiments as well as field observations. She applies her experimental findings to better understand natural hazards, with particular interest in earthquake hazards. Her work investigates where earthquakes occur and how rock properties influence the processes of earthquake nucleation, growth, and arrest. French's educational background includes a B.A. in Physics & Geology from Oberlin College, an M.S. in Geology from the University of Wisconsin - Madison, and a Ph.D. in Geophysics from Texas A&M University.

Research topics

• Petrology
• Seismology
• Geology
• Materials science
• Geochemistry
• Composite material
• Geotechnical engineering
• Geophysics
• Paleontology

Selected publications

• Data for article "Rheologic controls on the depth-dependence of megathrust earthquakes"

  Zenodo (CERN European Organization for Nuclear Research) · 2026-01-01

  datasetOpen access1st authorCorresponding

  The files contained in this folder either contain the data used in the manuscript "Rheologic controls on the depth-dependence of megathrust earthquakes" by French et al. or contain the code required to produce the figures. 1. Earthquakes folder contains up to 3 files per margin. One file contains all earthquakes downloaded from CMT near the transect studies, the other two which contain '7km_projected' or '12km_projected' in the name contain the earthquakes projected from within 75 km horizontal distance of the transect and then filter for those within 7 or 12 km normal to the slab top. 2. Temperature Profile files contain two columns: Temperature in C calculated using the England and May (2021) solution and input parameters stated in the manuscript and Depth in km. 3. Slab Profiles Contain the xz coordinates of each slab which were needed to calculate the temperature profiles. 4. Strength Profile Inputs contains the files needed to run the code to create strength profiles (StrengthProfileCalculations.m). These files contain depth (km) and temperature (K) directly from the thermal model outputs, overburden (bars), water pressure (bars) which is used to calcite the specific water volume (cc/mol) and water fugacity (bars). Specific water volume and fugacity are needed for dissolution precipitation creep calculations of the metasediments. 5. StrengthProfileCalculations.m can be used to calculate all strength profiles in the manuscript if the first 6 variables are adjusted to the appropriate values and in file read (M) is selected for the appropriate margin the Strength Profile Inputs folder.

  PublisherDOI

• Strength and Permeability of Pelagic Carbonate Sediments from the Northern Hikurangi Margin

  Zenodo (CERN European Organization for Nuclear Research) · 2026-03-05

  datasetOpen access

  Data for "Strength and Permeability of Pelagic Carbonate Sediments from the Northern Hikurangi Margin". Abstract: The shallow megathrust of the northern Hikurangi margin hosts both tsunami earthquakes and recurring slow slip events (SSEs), which are proposed to be influenced by both the abundance of subducting pelagic carbonates and stress perturbations due to subducting seamounts. To provide better constraints on the rheology and its control on slip mode, we measured the strength, healing behavior, and permeability of pelagic carbonate sediments recovered from IODP Expedition 375 Site U1520C. Experiments were performed on marl (29% clay) and chalk (6% clay) samples at effective pressures of 8, 21, and 70 MPa and temperatures of 25 and 75 °C, representative of the in-situ environment around the subducting Pāpaku Seamount. We conducted constant displacement rate and long duration (100-1,000,000 s) slide-hold-slide friction experiments, with flow through permeability tests prior to and after a subset of these. Our results show that the clay content in marl causes permeability to be 1-2.5 orders of magnitude lower than chalk, but less sensitive to effective pressure and shear strain. Because marl overlies chalk, its low permeability can maintain high pore fluid pressure thought to correlate with SSEs. More surprisingly, higher clay content corresponded to higher strength at multiple conditions that correlated with lower effective pressures and higher temperature, indicating that strain may partition into the chalk. We attribute this to inhibited mechanical compaction and chemical weakening with increasing clay content. We found a lack of Dieterich-type frictional healing in both lithologies, consistent with the low stress-drops of SSEs.

  PublisherDOI

• Strength and Permeability of Pelagic Carbonate Sediments from the Northern Hikurangi Margin

  Open MIND · 2026-03-05

  dataset

  Data for "Strength and Permeability of Pelagic Carbonate Sediments from the Northern Hikurangi Margin". Abstract: The shallow megathrust of the northern Hikurangi margin hosts both tsunami earthquakes and recurring slow slip events (SSEs), which are proposed to be influenced by both the abundance of subducting pelagic carbonates and stress perturbations due to subducting seamounts. To provide better constraints on the rheology and its control on slip mode, we measured the strength, healing behavior, and permeability of pelagic carbonate sediments recovered from IODP Expedition 375 Site U1520C. Experiments were performed on marl (29% clay) and chalk (6% clay) samples at effective pressures of 8, 21, and 70 MPa and temperatures of 25 and 75 °C, representative of the in-situ environment around the subducting Pāpaku Seamount. We conducted constant displacement rate and long duration (100-1,000,000 s) slide-hold-slide friction experiments, with flow through permeability tests prior to and after a subset of these. Our results show that the clay content in marl causes permeability to be 1-2.5 orders of magnitude lower than chalk, but less sensitive to effective pressure and shear strain. Because marl overlies chalk, its low permeability can maintain high pore fluid pressure thought to correlate with SSEs. More surprisingly, higher clay content corresponded to higher strength at multiple conditions that correlated with lower effective pressures and higher temperature, indicating that strain may partition into the chalk. We attribute this to inhibited mechanical compaction and chemical weakening with increasing clay content. We found a lack of Dieterich-type frictional healing in both lithologies, consistent with the low stress-drops of SSEs.

  DOI

• K‐Metasomatic Weakening of Oceanic Crust at Shallow Subduction Depths: Evidence From the Rodeo Cove Thrust Zone, Marin Headlands, California

  Geochemistry Geophysics Geosystems · 2025-07-01 · 1 citations

  articleOpen access

  Abstract Studies of exhumed subduction shear zones indicate that metamorphism and metasomatism of the oceanic lithosphere influence the composition, structure, and rheology of megathrust faults, particularly deep along the plate boundary (>30 km). However, less is known about the effects that fluid‐mediated chemical reactions have on the rheological evolution of oceanic crust at shallower depths, which may control diverse modes of fault slip and down‐stepping of the plate boundary into oceanic crust. Here, we present a structural and geochemical study of fault rocks from the Rodeo Cove thrust zone (RCT) in California to examine feedbacks between deformation and metasomatism of oceanic crust in a shallow subduction thrust environment (<15 km). At the RCT, deformation is accommodated by a dense network of reddish and greenish cataclasites, which surround altered basalt blocks containing abundant calcite veins and cement. Electron microprobe analyses show that the altered basalt is primarily composed of clinopyroxene, albite, chlorite, and pumpellyite, whereas the cataclasite is dominated by ferroaluminoceladonite (K‐ and Fe‐rich mica) and iron‐oxyhydroxides interlayered with well‐crystallized sheets of aluminoceladonite. Our findings suggest that subduction‐related faulting and cataclasis increased permeability within the basalt‐hosted shear zone, promoting extensive K‐metasomatism, first by oxidizing seawater and later by hydrothermal fluids sourced from subducted sediment and/or altered oceanic crust at greater depths. Moreover, contrasting deformation mechanisms between the less altered basalt and strongly K‐metasomatized cataclasite, combined with their constitutive properties quantified from deformation experiments, indicate that K‐metasomatism significantly decreased the frictional strength of oceanic crust causing strain to localize in the RCT.

  PublisherOA PDFDOI

• Rapid fault healing from cementation controls the dynamics of deep slow slip and tremor

  Science Advances · 2025-11-19 · 5 citations

  articleOpen access

  Despite its status as one of the most important discoveries in geophysics, the physical mechanism(s) responsible for slow slip events (SSEs) are not well understood. Here, we synthesize observations of deep SSEs in the Cascadia Subduction Zone and argue that rapid, cohesive fault strengthening may control the dynamics of deep SSEs. Cohesive strength is frequently ignored in constitutive laws used to describe fault rheology in numerical simulations of earthquakes and SSEs alike. To demonstrate its importance, we perform and analyze a suite of petrological experiments that simulate fault healing under representative pressure and temperature conditions. We show that significant cohesive strength recovery caused by dissolution-precipitation processes occurs on timescales of just a few hours. Together, our experimental and observational results support the idea that cohesion is a key component of fault strength under SSE conditions and highlight the need for its inclusion in both future experiments and numerical models of fault slip.

  PublisherDOI

• Data for article "Rheologic controls on the depth-dependence of megathrust earthquakes"

  Zenodo (CERN European Organization for Nuclear Research) · 2025-12-05

  datasetOpen access1st authorCorresponding
  PublisherDOI

• Using calcite deformation twins to constrain subduction-related paleostress state and deformation temperatures: A case study using the exhumed Sestola-Vidiciatico unit of the Northern Apennines, Italy

  Geosphere · 2025-10-02

  articleOpen access

  Abstract The Sestola-Vidiciatico unit (SVU) in the Northern Apennines, Italy, is an exhumed subduction interface with exposures that reached 200 °C, corresponding to ~9 km paleodepth. This unit experienced a relatively limited deformation history and serves as a rare analog to the shallowest sedimentary portions of active subduction megathrusts. We use the SVU as a case study of calcite twin analytical methods using calcite shear veins along mineralized faults surrounding the exhumed subduction interface. We reconstruct paleostress orientations through calcite twin stress inversion and use calcite twin paleopiezometry and geothermometry to reconstruct the stress state of the SVU during subduction and subsequent exhumation. We find that stress orientations are consistent between different faults using calcite twin stress inversion and calcite twin geothermometry yield consistent results with organic matter pyrolysis and vitrinite reflectance data, indicating these techniques work well for estimating paleostress orientations and temperatures. Furthermore, our findings are consistent with theoretical and geophysical studies for these tectonic regimes, whereby N- to NE-directed compression during subduction was followed by an inversion of stress orientations during exhumation. However, three of four tested paleopiezometers yield unreasonably high differential stresses, which we ascribe to averaging across a polyphase deformation history as well as differences between the laboratory experiments used to create the piezometers and natural deformation. In addition, calcite twin paleopiezometry and geothermometry suggest the inversion of principal stresses may have coincided with higher differential stresses during exhumation, and we consider possible explanations for this scenario including contrasting mechanical strength and changes in pore fluid pressures.

  PublisherOA PDFDOI

• Effects of Dilatant Hardening on Fault Stabilization and Structural Development

  Geophysical Research Letters · 2024-05-15 · 5 citations

  articleOpen accessSenior author

  Abstract Dilatant hardening is one proposed mechanism that causes slow earthquakes along faults. Previous experiments and models show that dilatant hardening can stabilize fault rupture and slip in several lithologies. However, few studies have systematically measured the mechanical behavior across the transition from dynamic to slow rupture or considered how the associated damage varies. To constrain the processes and scales of dilatant hardening, we conducted triaxial compression experiments on cores of Crab Orchard sandstone and structural analyses using micro‐computed tomography imaging and petrographic analysis. Experiments were conducted at an effective confining pressure of ∼10 MPa, while varying confining pressure (10–130 MPa) and pore fluid pressure (1–120 MPa). Above 15 MPa pore fluid pressure, dilatant hardening slows the rate of fault rupture and slip and deformation becomes more distributed amongst multiple faults as microfracturing increases. The resulting increase in fracture energy has the potential to control fault slip behavior.

  PublisherOA PDFDOI

• Determining the deformation temperatures and paleostress conditions of the Sestola-Vidiciatico Unit in the Northern Apennines, an exhumed shallow subduction zone, using calcite deformation twins

  2024-03-09

  preprintOpen access

  Understanding the stress conditions of active subduction zones has been a longstanding hurdle with critical implications for natural disasters considering stress/strain orientations and magnitudes can control shallow earthquakes and tsunamigenesis. The Sestola-Vidiciatico Unit (SVU) in the Northern Apennines is an exhumed subduction channel with exposures of up to 9 km paleodepth, having reached up to 200°C. This unit experienced a relatively limited deformation history and serves as a rare analog to the shallowest portions of active subduction megathrusts. We use calcite twin data from shear veins along mineralized faults surrounding the exhumed subduction interface to reconstruct paleostress orientations through calcite twin stress inversion. Combining orientation data with calcite twin paleopiezometry and geothermometry, we are able to reconstruct the stress state of the SVU during peak subduction and subsequent exhumation.During subduction, the maximum principal stress axis was oriented at a low angle to the subduction interface and the minimum principal stress axis oriented at a high angle, indicating N/NE directed compression. As subduction ceased and exhumation initiated, stress orientations inverted with the maximum principal stress axis becoming oriented at a high angle to the subduction interface and the minimum principal stress axis oriented at a low angle, indicating N/NE directed extension driven by primarily the weight of overburden material. These findings are consistent with theoretical orientations for both of these tectonic regimes and agree with previous studies interpreting subduction zone stress orientations. Calcite twin paleopiezometry and geothermometry suggests the rotation of principal stresses coincides with higher differential stresses during early exhumation. Based on the interpreted differential stresses and the reconstructed paleostress orientations, we model different possible explanations including contrasting mechanical strength between the contractional and extensional faults or changes in pore fluid pressure conditions between the two different tectonic regimes.

  PublisherDOI

• Path and Slip Dependent Behavior of Shallow Subduction Shear Zones During Fluid Overpressure

  Journal of Geophysical Research Solid Earth · 2024-04-01 · 2 citations

  articleOpen accessSenior author

  Abstract Elevated pore fluid pressure is proposed to contribute to slow earthquakes along shallow subduction plate boundaries. However, the processes that create high fluid pressure, disequilibrium compaction and dehydration reactions, lead to different effective stress paths in fault rocks. These paths are predicted by granular mechanics frameworks to lead to different strengths and deformation modes, yet granular mechanics do not predict their effects on fault stability. To evaluate the role of fluid overpressure on shallow megathrust strength and slip behavior, we conducted triaxial shear experiments on chlorite and celadonite rich gouge layers. Experiments were conducted at constant temperature (130 and 100°C), confining pressure (130 and 140 MPa), and pore fluid pressures (between 10 and 120 MPa). Fluid overpressure due to disequilibrium compaction was simulated by increasing confining and pore fluid pressure synchronously without exceeding the target effective pressure, whereas overpressure due to dehydration reactions was simulated by first loading the sample to a target isotropic effective pressure and then increasing pore fluid pressure to reduce the effective pressure. We find that the effects of fluid pressure and stress path on the mechanical behavior of the chlorite and celadonite gouges can generally be described using the critical state soil mechanics (CSSM) framework. However, path effects are more pronounced and persist to greater displacements in chlorite because its microstructure is more influenced by stress path. Due to its effects on microstructure, the stress path also imparts greater control on the rate‐dependence of chlorite strength, which is not predicted by CSSM.

  PublisherOA PDFDOI

Recent grants

• Controls of Pore Fluid Pressure on Fault Slip Weakening and Fracture Energy

  NSF · $265k · 2018–2024

• An Experimental Study on the Role of Pore Fluid Pressure During Slow Slip in Subduction Zones

  NSF · $169k · 2015–2017

• CAREER: Path Dependent Slip of the Shallow Subduction Megathrust

  NSF · $602k · 2020–2027

Frequent coauthors

• Céline Fliedner

  Rice University

  24 shared

• Cailey Condit

  21 shared

• Wenlu Zhu

  12 shared

• B. Belzer

  Rice University

  11 shared

• Jonathan R. Delph

  Purdue University West Lafayette

  9 shared

• J. S. Chester

  Texas A&M University

  9 shared

• F. M. Chester

  Texas A&M University

  8 shared

• Victor Guevara

  6 shared

Labs

• Rice Rock Deformation LabPI

Education

• PhD, Geology and Geophysics

  Texas A&M University

  2014

• MS, Geosciences

  University of Wisconsin System

  2009

• BA, Physics

  Oberlin College

  2006