Estimating along-strike variation of off-fault deformation for the 2018 Mw 6.4 Hualien earthquake
Journal
Geoscience Letters
Journal Volume
13
Journal Issue
1
ISSN
2196-4092
Date Issued
2026-03-30
Author(s)
Abstract
The assessment of surface deformation is one of the important aspects for understanding fault activity and disaster mitigation. While near-fault deformation has traditionally been documented using in-situ measurements, advances in optical image correlation now allow high-resolution quantification of both localized and distributed off-fault deformation (OFD) across fault zones. During the 2018 Mw 6.4 Hualien earthquake, rupture of the Milun fault—one of the most active structures in the Longitudinal Valley suture of eastern Taiwan—was accompanied by significant off-fault deformation, yet its along-strike variability has remained less well constrained. To characterize these variations, we derived high-resolution near-field displacement fields from pre- and post-earthquake aerial imagery using structure-from-motion technique and sub-pixel image correlation. The results show a clear left-lateral rupture with an average fault-parallel surface displacement of 0.94 m, but with pronounced along-strike differences in deformation style. Surface deformation is relatively localized in the northern segment, where off-fault deformation accounts for ~ 48% of the total displacement, whereas deformation becomes wider and more diffuse toward the south, with off-fault deformation increasing to ~ 87% and extending over widths exceeding 300 m. Elastic dislocation modeling suggests larger and shallower slip in the northern segment and progressively deeper slip burial in the south, consistent with enhanced distributed deformation in areas underlain by thicker, weaker sediments and where fault orientation is more oblique. Similar along-strike patterns observed in both the 1951 and 2018 Hualien earthquakes indicate that persistent structural and material controls govern strain partitioning along the Milun fault. These results highlight the importance of explicitly accounting for off-fault deformation and fault-zone width in seismic hazard assessments and near-fault engineering applications.
Subjects
Coseismic displacements
Earthquake
Milun fault
Surface rupture
Publisher
Springer Science and Business Media LLC
Type
journal article