Slip‐weakening distance and energy budget inferred from near‐fault ground deformation during the 2016 Mw7.8 Kaikōura earthquake

• Published in: Geophysical research letters Vol. 44; no. 10; pp. 4765 - 4773
• Main Authors: Kaneko, Yoshihiro, Fukuyama, Eiichi, Hamling, Ian James
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28-05-2017
• Subjects: Coastal environments; Deformation; Deformation mechanisms; Displacement; Dissipation; Distance; Dynamics; Earthquake accelerograms; earthquake energy budget; earthquake source physics; Earthquakes; Energy; Energy budget; Evolution; Fault lines; Integration; Kaikoura earthquake; Modularity; Movement; Numerical integration; Parameter estimation; Parameters; Propagation; Propagation velocity; Rupture; Rupturing; Scaling; Seismic activity; Servers; Shaking; Slip; slip‐weakening distance; Velocity; Waveforms; New Zealand; South Island New Zealand
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2017GL073681

The 2016 M7.8 Kaikōura (New Zealand) earthquake struck the east coast of the northern South Island, resulting in strong ground shaking and large surface fault slip. Since the earthquake was well recorded by a local strong‐motion seismic network, near‐fault data may provide direct measurements of dynamic parameters associated with the fault‐weakening process. Here we estimate a proxy for slip‐weakening distance
Dc′′, defined as double the fault‐parallel displacement at the time of peak ground velocity, from accelerograms recorded at a near‐fault station. Three‐component ground displacements were recovered from the double numerical integration of accelerograms, and the corresponding final displacements are validated against coseismic displacement from geodetic data. The estimated
Dc′′ is 4.9 m at seismic station KEKS located ∼2.7 km from a segment of the Kekerengu fault where large surface fault slip (∼12 m) has been observed. The inferred
Dc′′ is the largest value ever estimated from near‐fault strong motion data, yet it appears to follow the scaling of
Dc′′ with final slip for several large strike‐slip earthquakes. The energy budget of the M7.8 Kaikōura earthquake inferred from the scaling of
Dc′′ with final slip indicates that a large amount of energy was dissipated by on‐ and off‐fault inelastic deformation during the propagation of the earthquake rupture, resulting in a slower average rupture speed (
≲2.0 km/s).
Plain Language Summary
Slip‐weakening distance is a parameter controlling the evolution of fault slip during an earthquake and is important for understanding rupture dynamics. However, it has been debated how large slip‐weakening distance is and whether it scales with fault slip. We present evidence for large slip‐weakening distance estimated from near‐fault record of the recent magnitude 7.8 Kaikōura (New Zealand) earthquake. By examining seismic waveforms of the Kaikōura quake, we find that the slip‐weakening distance is about 5 m on a portion of the Kekerengu fault, the largest value ever estimated directly from near‐fault records. The large slip‐weakening distance implies that a large amount of energy was dissipated by on‐ and off‐fault inelastic deformation during the propagation of earthquake rupture, which may explain why the rupture propagation velocity of the Kaikōura quake was slower than that of most crustal earthquakes.
Key Points
We estimate a proxy for slip‐weakening distance
Dc′′ from near‐fault record of the 2016 M7.8 Kaikōura (New Zealand) earthquake
The
Dc′′ is 4.9 m at station KEKS, the largest value ever estimated from near‐fault strong motion data
The large
Dc′′ appears to follow the scaling
Dc′′ with final slip for several large strike‐slip earthquakes