Crustal Fault Connectivity of the Mw 7.8 2016 Kaikōura Earthquake Constrained by Aftershock Relocations

©2019. American Geophysical Union. All Rights Reserved. The 14 November 2016 Mw7.8 Kaikōura earthquake in the northern South Island, New Zealand, involved highly complex, multifault rupture. We combine data from a temporary network and the permanent national seismograph network to repick and relocate ~2,700 aftershocks of M≥3 that occurred between 14 November 2016 and 13 May 2017. Automatic phase-picking is carried out using REST, a newly developed hybrid method whose pick quality is assessed by comparing automatic picks for a subset of 138 events with analysts' picks. Aftershock hypocenters computed from high-quality REST picks and a 3-D velocity model cluster almost exclusively in the shallow crust of the upper plate and reveal linkages at depth between surface-rupturing fault segments. Only eight aftershocks are relocated on a deeper structure positioned between patches of geodetically detected afterslip. This indicates that afterslip has not triggered significant earthquake activity on the subduction interface during the period of aftershock activity analyzed.

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Variations in Seismogenic Thickness Along the Central Alpine Fault, New Zealand, Revealed by a Decade's Relocated Microseismicity

10.26686/wgtn.13792922.v1 ◽

2021 ◽

Author(s):

K Michailos ◽

EGC Smith ◽

Calum Chamberlain ◽

Martha Savage ◽

John Townend

Keyword(s):

Seismic Data ◽

Hanging Wall ◽

High Heat ◽

Earthquake Activity ◽

Alpine Fault ◽

Waveform Cross Correlation ◽

Uplift Rates ◽

American Geophysical ◽

Seismic Networks ◽

American Geophysical Union

©2018. American Geophysical Union. All Rights Reserved. The Alpine Fault is an oblique strike-slip fault that is known to fail in large magnitude (M7–8) earthquakes, yet it is currently seismically quiescent. We examine the low-magnitude earthquake activity occurring along the central portion of the Alpine Fault using seismic data from five temporary seismic networks deployed for various lengths of time between late 2008 and early 2017. Starting from continuous seismic data, we detect earthquake arrivals and construct the longest and most extensive microearthquake catalog for the central Alpine Fault region to date, containing 9,111 earthquakes. This enables us to study the distribution and characteristics of the seismicity in unprecedented detail. Earthquake locations are constrained by high-quality automatic and manual picks, and we perform relocations using waveform cross-correlation to better constrain hypocenters. We have derived a new local magnitude scale calibrated by M w values. Magnitudes range between M L −1.2 and 4.6, and our catalog is complete above M L 1.1. Earthquakes mainly occur southeast of the Alpine Fault (in the hanging wall) and exhibit low magnitudes. We observe a lack of seismicity beneath Aoraki/Mount Cook, which we associate with high uplift rates and high heat flow. Seismogenic cutoff depths vary along the strike of the Alpine Fault from 8 km, beneath the highest topography, to 20 km in the adjacent areas.

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Variations in Seismogenic Thickness Along the Central Alpine Fault, New Zealand, Revealed by a Decade's Relocated Microseismicity

10.26686/wgtn.13792922 ◽

2021 ◽

Author(s):

K Michailos ◽

EGC Smith ◽

Calum Chamberlain ◽

Martha Savage ◽

John Townend

Keyword(s):

Seismic Data ◽

Hanging Wall ◽

High Heat ◽

Earthquake Activity ◽

Alpine Fault ◽

Waveform Cross Correlation ◽

Uplift Rates ◽

American Geophysical ◽

Seismic Networks ◽

American Geophysical Union

©2018. American Geophysical Union. All Rights Reserved. The Alpine Fault is an oblique strike-slip fault that is known to fail in large magnitude (M7–8) earthquakes, yet it is currently seismically quiescent. We examine the low-magnitude earthquake activity occurring along the central portion of the Alpine Fault using seismic data from five temporary seismic networks deployed for various lengths of time between late 2008 and early 2017. Starting from continuous seismic data, we detect earthquake arrivals and construct the longest and most extensive microearthquake catalog for the central Alpine Fault region to date, containing 9,111 earthquakes. This enables us to study the distribution and characteristics of the seismicity in unprecedented detail. Earthquake locations are constrained by high-quality automatic and manual picks, and we perform relocations using waveform cross-correlation to better constrain hypocenters. We have derived a new local magnitude scale calibrated by M w values. Magnitudes range between M L −1.2 and 4.6, and our catalog is complete above M L 1.1. Earthquakes mainly occur southeast of the Alpine Fault (in the hanging wall) and exhibit low magnitudes. We observe a lack of seismicity beneath Aoraki/Mount Cook, which we associate with high uplift rates and high heat flow. Seismogenic cutoff depths vary along the strike of the Alpine Fault from 8 km, beneath the highest topography, to 20 km in the adjacent areas.

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