Location:

Magnitude:

7.5

Time:

28 Sep 2018 10:02:45

Depth:

20.0

There are 2 swarms found nearby.

2005

PS20050124.1(90.1km)

23 Jan

4 hours

5 earthquakes

2018

PS20180928.1(22.8km)

28 Sep

7 hours

15 earthquakes

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The 2018 Palu Earthquake: Geological Setting and Regional Context

On 28 September 2018 at 10:02 local time, a moment magnitude 7.5 earthquake struck 72 km north of Palu, Indonesia, at a focal depth of 20 km. This event represents the sole strong earthquake recorded in the immediate vicinity since 1 January 2000.

Sulawesi lies at the complex junction of the Australian, Philippine Sea, and Sunda plates. Oblique convergence is accommodated by a network of strike-slip and thrust faults. The dominant structure near Palu is the Palu-Koro fault, a mature left-lateral strike-slip system that trends northwest-southeast through the city and extends offshore into the Makassar Strait. Geodetic measurements indicate long-term slip rates of approximately 30–40 mm per year along this fault, consistent with its role in partitioning regional strain.

The 2018 rupture initiated on the Palu-Koro fault and propagated bilaterally for roughly 150 km. The shallow depth and proximity to the coastline produced intense ground shaking, widespread liquefaction in the Palu basin, and a local tsunami that inundated the city within minutes. Post-event field surveys documented maximum coseismic offsets exceeding 4 m, confirming the fault’s high slip potential.

Historically, the Palu-Koro fault has generated multiple large events, though instrumental records prior to 2000 remain sparse. Paleoseismic trenching indicates recurrence intervals on the order of several centuries for M ≥ 7 earthquakes, underscoring the fault’s capacity for infrequent but high-magnitude releases.

Following the 2018 mainshock, aftershock activity decayed rapidly, with the largest aftershock reaching only M 5.8. Ongoing geodetic monitoring shows continued post-seismic deformation along the fault trace, providing valuable data for refining regional seismic hazard models.

References

USGS Earthquake Catalog (event page for 2018-09-28 M7.5 Palu)
Global Centroid Moment Tensor (GCMT) solution for 2018 Palu earthquake
Geological Society of America, Special Paper 551: The 2018 Palu Earthquake Sequence