Victoria University of Wellington's Groundbreaking Discovery in Earthquake Dynamics

Researchers at Te Herenga Waka—Victoria University of Wellington have made a pivotal advancement in understanding how large earthquakes come to an end. Their study, freshly published in the prestigious journal Science, reveals a previously undetected 'stopping phase' that causes a dramatic reversal in ground motion, dubbed 'seismic whiplash'. This phenomenon occurs when massive strike-slip earthquakes halt abruptly, sending shockwaves backward along the fault line and intensifying shaking near the rupture's end.

Strike-slip earthquakes, where tectonic plates slide horizontally past each other along near-vertical faults, are among the most destructive. Examples include California's San Andreas Fault and New Zealand's Alpine Fault. Lead author Dr. Jesse Kearse, a Research Fellow in Earth Sciences at VUW's School of Geography, Environment and Earth Sciences, explained, "The magnitude of an earthquake depends on how far a rupture travels along a fault line before it stops. We've now directly observed this halting process for the first time."

This NZ-led research not only sheds light on global seismic behavior but holds particular relevance for New Zealand, a nation perched on the Pacific Ring of Fire with active faults like those threatening Wellington. By pinpointing where the fiercest shaking occurs—at fault segment boundaries and ends—the findings empower engineers and planners to bolster urban resilience.

Unveiling the Stopping Phase: The Science Behind Seismic Whiplash

Earthquakes begin when stress accumulated along a fault triggers a rupture that propagates at supersonic speeds, ripping through rock and releasing energy as seismic waves. While much is known about initiation, the termination process has remained elusive due to sparse near-fault data. VUW's team bridged this gap by analyzing high-resolution recordings from 12 major strike-slip earthquakes worldwide, including New Zealand's 2010 Darfield (magnitude 7.1) and 2016 Kaikōura (magnitude 7.8) events.

Using seismic sensors, Global Navigation Satellite System (GNSS) stations, and Interferometric Synthetic Aperture Radar (InSAR) satellite imagery placed mere kilometers from faults, the researchers detected a consistent 'negative phase' in ground motion at rupture endpoints. This stopping phase manifests as the ground suddenly jerking in the opposite direction to the primary slip—up to one meter backward in Kaikōura's case—over mere seconds.

Dr. Kearse likened it to a car slamming on brakes: "Your body lurches forward then snaps back, creating whiplash." Numerical simulations confirmed this signal only emerges from abrupt arrests; gradual deceleration produces no such reversal. The discovery challenges prior assumptions of smooth rupture decay, revealing dynamic barriers like fault bends or gaps that trigger the halt.

In the 2023 Turkey-Syria sequence, stopping phases appeared at segment edges, illustrating a 'domino cascade' where one section arrests before igniting the next. This stop-start pattern amplifies complexity in multi-segment ruptures common on systems like New Zealand's Alpine Fault.

New Zealand's Seismic Vulnerabilities Highlighted by VUW Findings

New Zealand experiences around 20,000 earthquakes annually, monitored by GeoNet, but few escalate to damaging scales. The VUW study spotlights local events: Darfield's rupture traversed multiple faults, while Kaikōura's hopped 170 kilometers across 12 segments, producing New Zealand's most complex modern quake.

Both exhibited pronounced stopping phases, with Kaikōura delivering meter-scale backward jolts near fault ends. This resonates deeply in Wellington, built atop active strike-slip features like the Wellington Fault. "Incorporating stopping phases into hazard models will refine predictions for cities near faults like our capital," Kearse noted.

The Alpine Fault, overdue for a magnitude 8 event (last in 1717), poses the nation's top threat. Comprising linked segments capable of cascading ruptures, it could unleash stopping phase whiplash across South Island communities. VUW's work equips GNS Science and local councils with tools to map high-risk zones at segment boundaries, enhancing evacuation and retrofitting strategies.

VUW's Expertise in Seismology Drives National Safety Advances

Te Herenga Waka—Victoria University of Wellington has long been a cornerstone of New Zealand's earthquake science. Home to the School of Geography, Environment and Earth Sciences, VUW hosts world-class facilities like the Wellington Seismology Research Centre and collaborates with GNS Science on GeoNet. Dr. Kearse's Tāwhia Te Mana Fellowship underscores VUW's commitment to Māori-led research, blending indigenous knowledge with cutting-edge geophysics.

Co-author Dr. Yoshihiro Kaneko complements this with expertise in dynamic rupture modeling. Their paper builds on VUW's legacy, including post-Kaikōura analyses that refined fault mapping. "VUW researchers are at the forefront of translating seismic insights into actionable policy," said Professor Mark Stirling, a VUW paleoseismologist not involved but praising the work.

The university's contributions extend to education: Earth Sciences programs train future seismologists, with hands-on fieldwork on local faults. Amid NZ's rising research profile—ranked top in QS for several subjects—VUW exemplifies how Kiwi innovation safeguards against 'The Big One'.

Engineering Implications: Whiplash Challenges for NZ Buildings

The stopping phase's velocity pulses and permanent offsets strain structures uniquely. Professor Charles Clifton (University of Auckland) noted, "We design for near-fault effects in key areas, but this expands locations needing consideration." Taller buildings sway excessively, risking cracks; base-isolated ones may fail if jolts exceed design limits.

Dr. Yusuke Mochida (University of Waikato) warned, "Sudden stops heavily strain high-rises, like a whip cracking." Dr. Shahab Ramhormozian (AUT) added nuance: "Abrupt termination may leave larger residual deformations in damaged structures." NZ's Earthquake Loadings Standard already addresses some fling effects, but VUW's data urges updates for segment edges.

Recent quakes (2010-2016) validated resilient designs in steel-framed buildings, but older retrofits face risks. Integrating stopping phases into models could prioritize reinforcements in Wellington's CBD and South Island towns near Alpine Fault segments. Expert reactions emphasize life-safety compliance while pushing resilience.

Global Reach, Local Impact: 12 Earthquakes Analyzed

• 2010 Darfield, NZ (M7.1): Multi-fault rupture with clear stopping signals.
• 2016 Kaikōura, NZ (M7.8): Extreme backward motion up to 1m, complex path.
• Turkey-Syria 2023: Segment cascades.
• Other global events confirming universality in strike-slip quakes.

Dense networks enabled detection; future dense deployments could extend to subduction zones like Hikurangi.

Future Directions: Enhancing NZ's Seismic Preparedness

VUW plans Hikurangi-focused studies to test stopping phases in subduction settings. Collaborations with Kyoto University bolster modeling. Policymakers should revise hazard maps, incorporating whiplash for Alpine Fault scenarios (75% chance M8+ in 50 years per prior GNS research).

Educational outreach via VUW's programs will train engineers; public awareness campaigns highlight fault-end risks. As NZ invests in resilience post-Kaikōura, this discovery accelerates progress.

VUW's Role in Fostering Seismic Innovation

With facilities like the Cotton Building labs, VUW pioneers seismogeodesy and InSAR. Kearse's Fulbright background enriches global ties. The university's ranking and funding (Royal Society fellowships) position it as NZ's seismic hub, producing graduates for GNS and engineering firms.

This Science publication elevates VUW internationally, attracting talent and grants for fault monitoring.

Photo by Jade Gray on Unsplash

In summary, VUW's seismic whiplash research transforms earthquake science, safeguarding Kiwis from nature's fury. By decoding rupture ends, it paves the way for smarter, safer builds amid NZ's restless geology.