Waikato Earthquake Faults: CT Scans Reveal Hidden Activity Risks

University of Waikato Researchers Revolutionize Seismic Detection with CT Scans

In a groundbreaking advancement for paleoseismology, scientists at the University of Waikato have employed medical CT scanners to peer into ancient lake sediments, revealing a history of hidden earthquake faults beneath the Hamilton Basin in New Zealand's Waikato region. This world-first technique has identified evidence of multiple large paleoearthquakes on previously obscured faults, challenging assumptions about the area's low-to-moderate seismic risk. Published on February 19, 2026, in the prestigious journal Science Advances, the study titled "Tephra seismites—Understanding seismic hazard of hidden faults by analyzing liquefied tephra layers in lakes" provides critical insights into Waikato earthquake faults that could generate significant shaking.

The Hamilton Basin, stretching approximately 80 kilometers from Ngāruawāhia to Te Awamutu and 50 kilometers wide, has long been viewed as a stable zone far from New Zealand's major plate boundary faults. However, discoveries since 2015 of buried faults like the Waikato Fault system prompted deeper investigation. Led by Emeritus Professor David Lowe, the research team analyzed sediment cores from 18 lakes formed around 20,000 years ago, uncovering deformation structures that serve as natural recorders of prehistoric seismic events. This not only enhances local hazard models but also opens doors for similar studies worldwide.

Unpacking Tephra Seismites: Nature's Earthquake Archives

Tephra seismites represent a novel proxy for past earthquakes, formed when volcanic ash layers—known as tephra (fine ejecta from eruptions like those of Taupō Volcano)—liquefy during intense ground shaking. Liquefaction occurs in loose, water-saturated sediments when seismic waves reduce grain friction, turning solid layers into fluid-like states that deform under overlying pressure. These structures, resembling downward-sagging loads or complex networks, solidify upon shaking cessation, preserving a snapshot of event intensity and location.

In the Hamilton Basin, 346 tephra layers spanning 1.7 to 17.5 thousand years were examined, with 127 exhibiting seismites. Their size and frequency increased toward known faults, enabling precise mapping. Tephrochronology—dating via unique ash geochemistry—provided exact timings, distinguishing seismic periods and linking deformations to specific ruptures. This method bypasses traditional trenching limitations on buried faults, offering a dense network of "seismographs" across the landscape.

CT Scans: A Medical Marvel Meets Earth Science

The innovation lies in adapting medical computed tomography (CT) scanners, typically used for human diagnostics, to image intact sediment cores. Researchers extracted 161 cores (1.5–2 meters long) from lakes like Lake Rotokaeo (Forest Lake), transporting them to I-MED Hamilton Radiology where radiographer Nic Ross scanned them at high resolution (0.625 mm voxels). Software like ImageJ processed the 3D volumes, revealing seismites invisible in 2D slices—such as intersecting loads up to 34 cm long.

Quantitative metrics included seismite occurrence ratio (SO) and length-to-thickness ratio (LT_av), interpolated via Kriging for severity maps. Peak ground acceleration (PGA) modeling correlated patterns to fault ruptures, estimating magnitudes from empirical relations. This non-destructive, high-fidelity approach marks a paradigm shift, applicable where volcanic tephras overlay fault-prone sediments.

Paleoearthquakes Mapped: A Timeline of Hidden Tremors

Analysis pinpointed two seismic periods (SP1 ~15.7–11.3 ka, SP2 post-7 ka) encompassing four major events (SE1–SE4):

• SE1 (~15.7–15 ka): Minimum M_w 7.4, linked to early fault activity.
• SE2 (~14–11.3 ka and post-1.7 ka): M_w 7.3–7.5 on Kerepehi–Te Puninga faults in Hauraki Plains, causing widespread liquefaction.
• SE3 (~7–4.3 ka): M_w 7.15 on Kūkūtāruhe fault, central Hamilton Basin.
• SE4 (post-1.7 ka): Minimum M_w 5.2+ on a newly inferred hidden fault southeast, within the last 1,800 years.

Mean recurrence of strong shaking: ~3,000 years, aligning with low-moderate hazard but underscoring potential for M7+ events.

Photo by Gaurav Kumar on Unsplash

The Culprit Faults: Waikato's Subsurface Network

Four active faults emerged as key players:

• Kūkūtāruhe Fault: Hidden in Hamilton lowlands, ruptured ~7–4 ka.
• Te Tātua ō Wairere Fault: Adjacent, potential extension.
• Te Puninga and Kerepehi Faults: Hauraki Plains, capable of M7.5, recurrence 3–11.5 ka.
• Unrecognized fault near Te Awamutu: Suggested by southeastern liquefaction zone.

Discovered via geomorphology in 2015, these align with the Waikato Fault system studied by GNS Science since 2021 through trenching. Integration into the New Zealand Community Fault Model refines national hazard assessments.

Seismic Hazard Reassessed: What It Means for Waikato

While short-term risk unchanged, long-term models now incorporate ~3 ka cycles, vital for Hamilton's growth (population hub, infrastructure corridor). Strong shaking could mirror Canterbury 2010 (MMI VII+ near faults), amplifying liquefaction in basin sediments. Updates aid resilient design for hospitals, power grids, and transport. Professor Lowe notes: "The probability is low by NZ standards, but not zero—risk grows with development."

Local iwi, councils, and agencies collaborated, funded by Marsden, MBIE, QuakeCoRE—exemplifying university-led hazard mitigation.

Global Reach: Exporting Waikato's Innovation

The CT-tephra method suits volcanic-tectonic zones like Auckland, Taranaki, Hawke's Bay, Iceland, Japan. It overcomes urban excavation barriers, using lake density (~1/20 km²) for high-resolution paleoearthquake catalogs. Future: Apply to turbidites, refine PGA relations for tephra.

For aspiring experts, University of Waikato offers PhD opportunities in geological modeling and seismic hazards, fostering careers in geoscience.Explore higher ed jobs in research.

The Waikato Team: Driving Excellence in Earth Sciences

Multidisciplinary effort: Dr. Max Kluger (lead author), Prof. David Lowe, Dr. Vicki Moon, Dr. Tehnuka Ilanko, Dr. Jordanka Chaneva (PhD alum), Prof. Rolando Orense, plus GNS's Dr. Pilar Villamor. Collaborators from University of Auckland, Swansea. Funded over four years, this underscores Waikato's prowess in Earth Sciences, preparing graduates for roles in hazard assessment and academia.University jobs in New Zealand.

Photo by Gaurav Kumar on Unsplash

From Faults to Preparedness: Actionable Insights

Dr. Villamor urges: "Prepare with plans and kits—even unlikely events demand readiness." Enhanced models bolster NZ's resilience amid population pressures. For students eyeing seismic research, Waikato exemplifies opportunity.Higher ed career advice on research paths abounds. This study not only illuminates Waikato earthquake faults but fortifies futures.