New Zealand southern Hikurangi earthquake catalogue 1990-2000 relocated with 3-D velocity model nzwide2.3, for article: EPSL 2009 Hikurangi earthquakes

This archive provides hypocenters for the period 1990-2000, related to the paper “Small earthquakes provide insight into plate coupling and fluid distribution in the Hikurangi subduction zone, New Zealand”, published in Earth and Planetary Science Letters (Reyners and Eberhart-Phillips, 2009). That research considered earthquakes 1990-2005. For the 2001-2011 period, relocated earthquakes have been previously archived on Zenodo, doi:10.5281/zenodo.6604627. The hypocenter locations use P- and S-wave arrival times from earthquakes during 1990-2000, which were manually picked with assigned quality. The Simul program is used (Eberhart-Phillips et al., 2024), and the current version of the New Zealand wide 3-D velocity model, nzwide2.3 (Eberhart-Phillips et al., 2022). The catalogue updates the nzwide1.0 hypocentres presented in Reyners and Eberhart-Phillips (2009), and results are similar. The hypocentre ‘xyze’ file includes various location quality parameters, and assigned letter quality codes as described in Table 1 (Eberhart-Phillips and Reyners, 2022). The location error computed in Simul is related to the diagonal of the covariance multiplied by a factor sig2, which should be related to the error in travel-time observations. The travel-time error is related both the measurement accuracy and the phase uncertainty, which Simul uses as the input reading error (rderr) and wrms, related by an error coefficient (ercof). sig2 = rderr*rderr + ercof*wrms In this work, we assign rderr as 0.05 s, and use ercof of 0.5 to provide larger location uncertainty for poorly-fit travel-time data. Further we assign erz as 20 km for fixed depth relocations, and set the maximum erh and erz to 99 km. We also assign minimum erh and erz for qualities C, D and E; since some computed location errors may be unrealistically small, as it is easier to fit a small set of observations, although the other quality parameters point to poorer actual constraint. For C quality, minimum erh is 1.0 and erz is 2.0. For D quality, minimum erh is 1.5 and erz is 3.0. For E quality, minimum erh is 2.0 and erz is 4.0. The New Zealand seismic network is sparse, with 100-km spacing, in some regions. Thus even the lower quality hypocentres contribute to understanding regional seismic potential. For seismicity cross-sections, Reyners and Eberhart-Phillips (2009) used the criteria rzdm ≥ 0.5, which is a key factor for depth constraint. To obtain numerous such events with the sparse 1990s network, selecting A,B,C events with rzdm ≥5 would be appropriate. Table 1. NZ-wide Assigned Quality Codes parameter A B C D E nobs ≥ 15 ≥ 12 ≥ 8 ≥ 6 ≥ 4 ns ≥ 4 ≥ 2 ≥ 1 wrms (s) ≤ 0.2 ≤ 0.3 ≤ 0.4 ≤ 0.6 gap (deg) ≤ 140 ≤ 180 ≤ 240 ≤ 270 dmin (km) ≤ 500 ≤ 500 ≤ 500 ≤ 500 rzdm (depth/dmin) ≥ 0.5 ≥ 0.3 ≥ 0.1 erh (km) ≤ 1.5 ≤ 2.5 ≤ 4 ≤ 8 erz (km) ≤ 2.5 ≤ 4 ≤ 6 ≤ 12 Archived files are: hypnzw23R1990_2000.xyze, the Simul hypocentre file with X,Y coordinates, error parameters and quality code. Table S1 shows a sample portion of this file. This can be read with the following fortran lines, where the file is assigned to fort.7. read(7,1631) iyr4,imo,idy,ihr,imin,sec,rlat,rlon,depth,rmag, 2 nobs,wrmsr,x,y,gap,dmin,rzdm,np,ns,serot,serh,serz,qcode 1631 format(i4.4,2(1x,2i2.2),f6.2,f9.4,f10.4,f7.2,f6.2, 2 i5,f6.2,2f9.2,i5,i4,f5.1,2i4,3f6.2,2x,a1) hypnzw23R1990_2000.sum, the Hypo71 summary format hypocentre file (Lee and Lahr, 1975). aznzw23Ra......out files in the tar file azlist.tar.gz. These are monthly output files in the Hypo71 list format that show the hypocentre solution, and stations travel-time, with remark, distance, azimuth, residual, and weight. f4nzw23Ra.......out files in the tar file ttdata.tar.gz. These Simul format travel-time data monthly output files provide the travel-times and phase remarks for each event.