Tectonic interpretation of aftershock relocations in eastern Papua New Guinea using teleseismic data and the arrival pattern method

Abstract

S U M M A R YThe arrival pattern (AP) method and teleseismic data have been used to relocate aftershocks following three major (M w >= 7.8) interplate earthquakes that occurred in eastern Papua New Guinea in 2000 November. The first event was an M w = 8.0 strike-slip earthquake that ruptured the Weitin fault over a length of ∼100 km. No aftershocks were located in the upper 15 km, suggesting that the accumulated strain was fully released in this event. The two subsequent M w = 7.8 thrust events occurred on the New Britain trench. Wadati-Benioff zones dipping ∼20 • define the locations of the thrust events at 152 • E and 153 • E on fault planes with strikes of 75 • and 65 • , respectively. The plot of aftershocks defines a complex seismic zone beneath New Ireland where events have occurred in the overriding Pacific and South Bismarck plates above the deeper zone of subduction of the Solomon Sea Plate. These events cluster in a broad zone to the northeast of the Weitin fault rather than defining a linear feature that might have been expected following a near-vertical major strike-slip event.

The Weitin Fault, Papua New Guinea, Ruptured Twice by Mw 8.0 and Mw 7.7 Earthquakes in 2000 and 2019

“…The stress drop there could have been incomplete in 2000, leaving some stresses to be released in 2019. This would contrast with the analysis of Tregoning et al () who noticed very little aftershock activity along the Weitin fault following the 2000 event. They interpreted this feature as an indication of complete stress release during the 2000 New Ireland earthquake sequence.…”

“…Measurements at two campaign GPS stations on each side of the fault and separated by <13 km show 8 m of left-lateral relative displacement (Tregoning et al, 2001;Tregoning et al, 2005; reported also in Figure 1). Vertical displacements are also consistent with a causative fault dipping to the northeast, where the site northeast of the Weitin fault was uplifted by ∼18 cm, while the site to the southwest subsided by ∼26 cm.…”

Triggering of earthquakes during the 2000 Papua New Guinea earthquake sequence

“…Almost all moderate and large earthquakes located near the subduction interface with this typical mechanism are observed to occur on the shallowly dipping plane. Also relocated aftershocks by Tregoning et al [2005] showed that both the 16 November B and 17 November events were plate boundary thrust events on the New Britain subduction zone defined by 20° dips on the Wadati‐Benioff zones.…”

“…There were observed strike‐slip surface displacements of up to 5 m along the fault on the east side of New Ireland (I. Itikarai, personal communication, 2001). GPS observation also showed left‐lateral movement up to 8 m along the Weitin‐Kamdaru fault [ Tregoning et al , 2005]. Tsunamis with heights up to 3 m were reported along the coasts of New Ireland, New Britain, and Bougainville (ISC catalogue).…”

An extension of the E/M0 tsunami earthquake discriminant Θ to regional distances

“…This thrust‐dominated M w = 8.0 (12.4 × 10 27 dyn cm) earthquake (Event 21), which ruptured the Weitin Fault between New Britain and New Ireland at the South Bismarck–Pacific Plate boundary (Tregoning et al 2005), was followed during the next 2 d by two large interplate aftershocks triggered by static stress changes induced by the main shock (Geist & Parsons 2005). Our mainstream corrected regional () and teleseismic Θ values () reflect the slightly slow but otherwise unremarkable nature of the main shock.…”