Discovery of a Hidden Strike-Slip Fault from High-Resolution Analysis of the 2019 Wang Nua Earthquake Sequence, Lampang, Northern Thailand

Buphu, Saowapak; Pananont, Passakorn; Furlong, Kevin P.; Pornsopin, Patinya

doi:10.3390/geosciences16050202

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Discovery of a Hidden Strike-Slip Fault from High-Resolution Analysis of the 2019 Wang Nua Earthquake Sequence, Lampang, Northern Thailand

¹

Department of Earth Sciences, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand

²

Thai Meteorological Department, Bangkok 10260, Thailand

³

Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA

^*

Author to whom correspondence should be addressed.

Geosciences 2026, 16(5), 202; https://doi.org/10.3390/geosciences16050202

Submission received: 27 March 2026 / Revised: 7 May 2026 / Accepted: 12 May 2026 / Published: 19 May 2026

(This article belongs to the Special Issue Earthquake Geology of Plate Margins and Plate Interiors: Integrating Classical Methods with New Approaches)

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Abstract

The M_L4.9 Wang Nua earthquake on 20 February 2019 is the largest earthquake to occur in Lampang Province in the past four decades and identifies the potential seismic hazard of previously unmapped faults in northern Thailand. We reanalyzed this earthquake sequence using waveform-based matched-filter detection and double-difference relocation techniques. The enhanced catalog increases the number of small earthquakes by 2.5 times compared with the official record. It also reveals microearthquakes down to M_L–0.3, including a previously unreported foreshock sequence beginning approximately four hours before the mainshock. Relocated hypocenters define an 8 km long, near-vertical N-S striking rupture zone at depths of 0.7–10.6 km. The focal mechanism of the mainshock indicates right-lateral strike-slip motion (strike ~189°, dip ~77°, rake ~–150°), aligned with the kinematics of other extensions of the Phayao Fault Zone. These results indicate that the sequence occurred on a previously unrecognized fault segment. This highlights the importance of high-resolution seismic analysis for improving hazard assessment in regions with concealed fault systems

Keywords: seismicity; matched-filter detection; earthquake relocation; earthquake sequence; Phayao Fault Zone; Lampang Thailand

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MDPI and ACS Style

Buphu, S.; Pananont, P.; Furlong, K.P.; Pornsopin, P. Discovery of a Hidden Strike-Slip Fault from High-Resolution Analysis of the 2019 Wang Nua Earthquake Sequence, Lampang, Northern Thailand. Geosciences 2026, 16, 202. https://doi.org/10.3390/geosciences16050202

AMA Style

Buphu S, Pananont P, Furlong KP, Pornsopin P. Discovery of a Hidden Strike-Slip Fault from High-Resolution Analysis of the 2019 Wang Nua Earthquake Sequence, Lampang, Northern Thailand. Geosciences. 2026; 16(5):202. https://doi.org/10.3390/geosciences16050202

Chicago/Turabian Style

Buphu, Saowapak, Passakorn Pananont, Kevin P. Furlong, and Patinya Pornsopin. 2026. "Discovery of a Hidden Strike-Slip Fault from High-Resolution Analysis of the 2019 Wang Nua Earthquake Sequence, Lampang, Northern Thailand" Geosciences 16, no. 5: 202. https://doi.org/10.3390/geosciences16050202

APA Style

Buphu, S., Pananont, P., Furlong, K. P., & Pornsopin, P. (2026). Discovery of a Hidden Strike-Slip Fault from High-Resolution Analysis of the 2019 Wang Nua Earthquake Sequence, Lampang, Northern Thailand. Geosciences, 16(5), 202. https://doi.org/10.3390/geosciences16050202

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Discovery of a Hidden Strike-Slip Fault from High-Resolution Analysis of the 2019 Wang Nua Earthquake Sequence, Lampang, Northern Thailand

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