Abstract:
This study deals with Auckland’s faulting in morphotectonic and geotechnical perspective. Remote Sensing (R/S) and Geographical Information System (GIS) techniques are used to map potential fracture system directional patterns, determine any faults exhibiting evidence of Quaternary or Holocene activity or have increased potential for future rupture, and explore the brittle geological strength of East Coast Bays Formation (ECBF) sandstone fractured rocks. A synthesis of the tectonic framework of Auckland is achieved using available geological and tectonic data, and integrating them with the output of a comprehensive multi-scale lineaments / linear features morphotectonic mapping by the interpretation of dynamically merged LiDAR data, Landsat-5 and Sentinel-2 space multispectral imagery, surrounding bathymetric data, and topographic maps. Successful neutralisation for the heavy vegetation cover mask in Auckland is achieved by selecting quality images, applying accurate enhancement, and implementing dynamic merge interpretation technique. Interpreted lineaments-fractures significance is verified in Wairoa North fault sub-area as a case study. A GIS database is compiled for the synthesised data using ArcGIS software package to produce an integrated morphotectonic map using database components to present directions of lineaments and linear features trends, investigated morphotectonic block zones, documented active faults, and zones of drainage anomalies as indicators of possible tectonic activity in the study area. Analysis for the lineaments and linear features to delineate potential fracture system characteristics is carried in light of recognised regional tectonic field stress orientation of New Zealand’s northern North Island. The direction of documented regional Maximum Horizontal Stress (SHMax) and the regional tectonic setting outlined major fracture trends and faults with potential mode of activity or possible rupture. Those trends are N00°-10°E, N50°-70°E, and N30°-50°W. Field mapping of the geotechnical characteristics of East Coast Bays Formation (ECBF) sandstone rocks is carried out in three case study locations of Auckland. Mapping comprised fractures orientation measurements, description of the rock mass using (NZGS, 2005) standards, and acquisition of the Uniaxial Compressive Strength (UCS) of the rocks. Geotechnical analysis for the field data revealed that some fracture trends are identical with the mapped N00º-10ºE, N50º-70ºE, and N30º-50ºW morphotectonic lineaments and linear features directions, and the general Geological Strength Index (GSI) ranges from 20 to 30. UCS showed lower values for rocks with intensive fracture intersections, extensional and shear oblique faults, and adjacent to fault planes.