DOI: 10.5281/zenodo.15858366
title: Supplementary files to "Focal mechanisms in the southeastern South Island of Aotearoa New Zealand indicate scale-dependent partitioning of transpressional strain"

description: This repository includes supplementary material to the in review artice

Williams, J., Eberhart-Phillips, D., Bourguignon S., Stirling, M., Reyners, M., Upton, P., Focal mechanisms in the southeastern South Island of Aotearoa New Zealand indicate scale-dependent partitioning of transpressional strain. In review with Seismica

Contents of this repository are:



bb_plots_otago.zip & bb_plots_sosa.zip: plots of the 103 and 30 focal mechanisms resolved from the Otago array and Southland Otago Seismic Array (SOSA) data using HASH (Hardback and Shearer 2002). Focal mechanisms are plotted in sets of 4. The focal mechanisms are plotted as in Figure 2 in the main text, so that for each event, the first column depicts the recording stations's projection and polarity in a lower hemisphere equal area stereonet, the P- and T-axes of the preferred and accepted nodal planes, and the preferred nodal planes. In the centre column, we show the S-wave/P-wave amplitude ratio at each event's recording station, and the preferred and accepted nodal planes. The right column depicts the preferred focal mechanism as a beach ball plot. The letters A-D after 'Q' in the event label indicate the focal mechanism quality (Table 2, main text).

combined_nodal_planes.csv: catalog of 133 focal mechanisms obtained from the Otago array and Southland Otago Seismic Array (SOSA). For A-C quality events, indicated nodal plane is the one selected by STRESSINVERSE as the preferred 'nodal plane' (Vavryčuk 2014). For D quality events, the default nodal plane returned by HASH is indicated. Event quality A-D criteria are described by Table 2 in the main text.

ref_instability_info.csv: list of the instability, I,  for each SOSA and Otago array focal mechanism within the stress state resolved by STRESSINVERSE's first and final iteration. Focal mechanism instability is defined following Eq. 13 in Vavryčuk (2014). This file also indicates which nodal plane is selected for the final stress inversion.

snz_rmt_nodal_planes.csv: catalog of events in the southeastern South Island from the GeoNet regional moment tensor catalog (Ristau et al 2013; https://github.com/GeoNet/data/tree/main/moment-tensor) up to 28/02/2025. The listed nodal planes are those selected as the 'preferred' nodal plane in STRESSINVERSE (Vavryčuk 2014).

SuppFigsS1-S3.pdf: This file contains the following figures: (Fig S1) histograms for the focal mechanism and region moment tensor event magnitudes documented in this study, histograms for the stress shape ratio (R) returned by 100 stress inversions of randomly sampled (Fig S2) Otago and SOSA focal mechanisms and (Fig S3) regional moment tensors. 


Any questions, please contact: jack.williams@otago.ac.nz

References



Hardebeck, J. L., & Shearer, P. M. (2002). A new method for determining first-motion focal mechanisms. Bulletin of the Seismological Society of America, 92(6), 2264-2276.

Ristau, J. (2013). Update of regional moment tensor analysis for earthquakes in New Zealand and adjacent offshore regions. Bulletin of the Seismological Society of America, 103(4), 2520-2533.

Vavryčuk, V. (2014). Iterative joint inversion for stress and fault orientations from focal mechanisms. Geophysical Journal International, 199(1), 69-77.