Plate-rate experimental deformation: Aseismic, transient or seismic fault slip

Project Information

PREDATORS

Grant agreement ID: 714430

DOI

10.3030/714430

Project closed

EC signature date 15 November 2016

Start date 1 March 2017

End date 31 December 2023

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 499 250,00

EU contribution

€ 1 499 250,00

Coordinated by

UNIVERSITAET BREMEN
Germany

Periodic Reporting for period 5 - PREDATORS (Plate-rate experimental deformation: Aseismic, transient or seismic fault slip)

Reporting period: 2023-09-01 to 2023-12-31

Summary of the context and overall objectives of the project

The main focus of the project is understanding natural geologic disasters, primarily earthquakes. Large magnitude earthquakes are one of the world’s greatest risks to human life and damage to infrastructure and economy in densely populated regions. The hazard is compounded by the fact that these events can cause other natural disasters such as enormous tsunamis. Recently, earthquakes induced by humans, for example from wastewater injection associated with oil and gas extraction, have become a source of concern to the public.
Describing the slip behavior of major fault zones relies heavily on the results of laboratory shearing experiments simulating fault slip. The seismic behavior of major faults depends not only the absolute strength of a fault, but also how strength changes as a function of time and slip velocity. Such behaviors are measurable in laboratory friction experiments, which have provided the framework for assessing the in-situ fault conditions and fault rock properties that allow earthquakes nucleate and propagate.
Despite the many advances in knowledge over the years, the tendency for faults to host earthquake slip (or not, in the case of creeping faults) is far from well understood. I identify this missing fundamental piece of information as how faults slip when driven at plate-convergence slip rates. Furthermore, there is a need to conduct experiments on real samples from natural faults, in addition to analogue materials used as laboratory standards. To do this, we take advantage of a large suite of sample obtained by scientific drilling at plate-boundary fault zones recovered by the Integrated Ocean Drilling Program (IODP) and International Continental Scientific Drilling Program (ICDP).
To summarize, the main goals of this project are to: (1) Quantitatively describe the slip behaviour of geologic materials –both natural and analogue fault rocks – when driven at plate tectonic convergence rates as they are in nature, in order to explain seismologic and geodetic observations on real faults and predict fault slip behaviour in the future; and (2) Identify the important factors controlling the range of observed modes of fault slip, in other words, to identify the processes or material characteristics are important for causing aseismic creep, slow slip events, or locking and coseismic slip.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project goals have been largely achieved. Specifically, this includes achievement of several of the “Deliverables” named in the Grant Agreement Annex.
A comprehensive dataset of frictional behavior for natural fault zone samples at cm/yr slip rates has been produced (Ikari and Kopf, 2017; Ikari, 2019). In addition, this dataset has been extended to five orders of magnitude faster velocities, for a total of 13 natural fault zone samples (Ikari, 2022 AGU Fall Meeting).
We have synthesized results of our plate-rate shearing velocity technique with geophysical observations (seismologic and geodetic) for site-specific studies of natural fault zones. These studies are intended to: (1) explain current geophysical observations on fault zones which are specifically tested in this study, and (2) help predict fault behavior at locations where sampling and geologic characterization is limited.
Several of these studies focused on the Hikurangi subduction zone offshore New Zealand, addressing the origin of slow slip events which are well-documented in the area (Rabinowitz et al., 2018; Ikari, Wallace et al., 2020; Eijsink and Ikari, 2022; Shreedharan et al., 2022). Another study focused on the lack of shallow seismic activity at the northern Cascadia subduction zone, discussing the possibility that the fault zone may not be locked (Stanislowski et al., 2022). Using slow, but not quite as low as plate-rate velocities, we have produced studies showing how natural samples from the Nankai subduction zone offshore Japan can produce shallow slow slip events (Roesner et al., 2020; Okuda et al., 2021; Roesner et al., 2022), which have been observed with borehole pressure sensors.
Results of innovative measurements have been produced and published. We have developed a new testing protocol that we call a “velocity-cycling” test, which is a hybrid of conventional slide-hold-slide and velocity-step tests that specifically simulates active loading from driving rates as low as mm/yr during the interseismic period (Ikari, Carpenter et al., 2020). We have also produced successfully simulated lithification in the lab by adding salt to sediment and desciccated the sample, creating synthetic rocks from sediment powder. Using this technique combined with our unique capability of directly measuring cohesion, we show how lifthification process can enable earthquakes (Ikari and Hüpers, 2021). Another study produced a first quantitative relation between fault surface roughness and friction parameters, which can be scaled directly from the lab to the field (Eijsink et al., 2022). We have also developed a technique to modify apparatus stiffness in both the normal and shear directions, producing a wide range of slip events (Eijsink and Ikari, 2024).
For added value, we have carefully documented the stiffness of our apparatus over a wide range of conditions, which is neglected in the literature, and published this as a technical report (Ikari and Haberkorn, 2023).
Several studies are still in progress at the time of this report, and are expected to be completed and published in the future. These include a study examining the role of mineral surface chemistry in fault slip behavior (Ikari and Conin, 2024 EGU General Assembly), extending the conditions of the plate-rate experiments to higher pressures and temperatures (Zhang et al., 2023 AGU Fall meeting), and an intriguing study suggesting that SSEs can be used for earthquake early warning (Ikari, 2023 EGU General Assembly).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The results of this project have been impactful and advanced the state of the art in the field of earthquake science. Friction data obtained at plate-rate driving velocities was very rare and did not exist before, and certainly not for natural fault samples. Thanks to this project, there is now a large database of friction at such low velocities, which now also spans up to 5 orders of magnitude faster, covering the entire range from plate-rate to conventional friction experiments. Although not quite as comprehensive, progress was made in extending the conditions at which the plate-rate friction was obtained, for stresses up to 30 MPa, temperatures up to 80 °C, and fluid pressures of ~ 1 MPa.

We have also made great progress on understanding the causes of the fault slip behavior we observe, both in the lab and in nature. Project research shows that important factors controlling earthquake vs. non-earthquake slip include surface roughness, lithification processes, the presence of high-grade minerals, and the electric charge of mineral surfaces.
For natural fault zones, our work has provided explanations geophysical and geodetic observations in Japan, New Zealand, USA/Canada, Indonesia, and Central America. These include why earthquake slip can happen so close to the Earth’s surface, and confirming hypotheses for the origin of slow slip events. Last but not least, we may have evidence that slow slip events can be used for earthquake early warning, which may end up being the most impactful discovery.

summary of experimental data, with selected sample images