Geologic, earthquake and tsunami modelling of the active Cape Egmont Fault Zone

The Cape Egmont Fault Zone in the southern Taranaki Basin, New Zealand, is a complex series of synthetic and antithetic dip-slip normal faults accommodating present-day extension. The fault zone comprises new and reactivated faults developed over multiple phases of plate boundary deformation during the last 100 Myrs. The fault zone is well imaged on petroleum industry seismic reflection data, with a number of faults exposed and studied onshore.

The Cape Egmont Fault Zone is seismically active, with damaging historic earthquakes of up to Mw 5.4. Most earthquakes occur beneath the Late Cretaceous to Holocene sedimentary sequence at depths greater than 5–8 km. The maximum depth of fault rupture is c. 20 km, above which 90% of recorded earthquakes occur. Focal mechanisms from these earthquakes generally indicate strike-slip to oblique-normal faulting, which contrasts with the predominantly dip-slip faulting observed in the overlying sedimentary sequence and surface fault traces. Data from regional earthquake studies and petroleum well deformation show faults imaged in the sedimentary sequence to be preferentially oriented for slip in the present-day stress field.

The greatest earthquake risk is on major basement-penetrating crustal-scale faults greater than 20 km in length. Fault lengths and maximum vertical offsets of the sedimentary sequence, determined from a three-dimensional structural model, are consistent with global displacement-length scaling relationships. This validation permits fault lengths to be used to determine potential future earthquake magnitudes using global fault length-magnitude relationships. Fault lengths of post-Pliocene normal faults are typically ≤21 km, resulting in maximum predicted magnitudes Mw 6.3. The most likely earthquake magnitude from the fault population sampled is Mw 5.4 ± 0.5. The largest and most mature fault – the Cape Egmont Fault – is at least 53 km long and, depending on the number of segments ruptured during a future event, is capable of generating an earthquake between Mw 7 and 7.3.

New sub-surface radiometric ages constraining the age of the ring plain created by Taranaki Maunga and its predecessors support 3 Myrs of continuous volcanism in the region.

Hornblende from 14 igneous samples from onshore petroleum exploration wells have yielded 40Ar/39Ar plateau ages ranging from c. 2.9 Ma to 0.15 Ma. Seven 40Ar/39Ar samples from near the base of the Taranaki Maunga ring plain (previously dated at <0.2 Ma) ranged from 0.515 Ma in the Kapuni-15 well on the south side of Taranaki to 0.39 Ma in Rahotu-1 on the western side. These data suggest that surficial volcanism, including Taranaki Maunga, initiated between 0.5 to 0.4 Ma.

DOI: https://doi.org/10.21420/ED9K-EP20

Cite data as:

Seebeck H, Thrasher GP, Viskovic GPD, Macklin C, Bull S, Wang X, Nicol A, Holden C, Kaneko Y, Mouslopoulou V, Begg JG. 2021. Geologic, earthquake and tsunami modelling of the active Cape Egmont Fault Zone. Lower Hutt (NZ): GNS Science. 370 p. (GNS Science report; 2021/06). doi:10.21420/100K-VW73.

(with data available at DOI: https://doi.org/10.21420/ED9K-EP20 )

Thrasher GP, Viskovic GPD, Sagar M, Seebeck H. 2024. Subsurface igneous rocks of the Taranaki Peninsula. Lower Hutt (NZ): GNS Science. 77 p. (GNS Science report; 2023/47). https://doi.org/10.21420/8BEH-6P24.

(with data available at DOI: https://doi.org/10.21420/ED9K-EP20 )

Date (Publication): 2022-06-03

Purpose: ***********************

Status: Completed

Point of contact

Organisation name	Individual name	Electronic mail address	Role
GNS Science		h.seebeck@gns.cri.nz	Point of contact

Maintenance and update frequency: Not planned

Theme

Cape Egmont Fault Zone
Earthquakes
Fault source model
Earthquake simulation
Tsunami simulation

Place

Taranaki Basin

Keywords

Subsurface radiometric volcanic rock ages

Classification: Unclassified

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Other constraints: (C) Institute of Geological and Nuclear Sciences Limited.

This material is licensed under a Creative Commons Attribution International 4.0 (CC BY 4.0) Licence. For more details visit https://creativecommons.org/licenses/by/4.0/.

Where the data are used in a figure GNS Science requests attribution in the following manner: (C) GNS Science. Where reference to the data is to be included in a Reference List the following citation is suggested:

Seebeck H, Thrasher GP, Viskovic GPD, Macklin C, Bull S, Wang X, Nicol A, Holden C, Kaneko Y, Mouslopoulou V, Begg JG. 2021. Geologic, earthquake and tsunami modelling of the active Cape Egmont Fault Zone. Lower Hutt (NZ): GNS Science. 370 p. (GNS Science report; 2021/06). doi:10.21420/100K-VW73.

Use constraints: Other restrictions

Other constraints: The report carries the following limitation, which also applies to this dataset:

"The Institute of Geological and Nuclear Sciences Limited (GNS Science) and its funders give no warranties of any kind concerning the accuracy, completeness, timeliness or fitness for purpose of the contents of this report. GNS Science accepts no responsibility for any actions taken based on, or reliance placed on the contents of this report and GNS Science and its funders exclude to the full extent permitted by law liability for any loss, damage or expense, direct or indirect, and however caused, whether through negligence or otherwise, resulting from any person’s or organisation’s use of, or reliance on, the contents of this report."

Language: English

Topic category

Geoscientific information

Begin date: 2018-10-01

End date: 2021-03-31

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WWW:DOWNLOAD-1.0-http--download	https://huta22.gns.cri.nz/metadata/srv/api/records/c9b2ba03-953b-4a38-ba43-95da772b326a/attachments/CEFZ_Tsunami_simulation_movie.zip
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Metadata language: English

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Hierarchy level: Dataset

Hierarchy level name: Dataset

Date stamp: 2024-06-26T01:27:34.04108Z

Metadata standard name: ISO 19115:2003/19139

Metadata standard version: 1.0

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Organisation name	Individual name	Electronic mail address	Role
GNS Science		datamanagement@gns.cri.nz	Point of contact

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