Location:

Period:

22 Jul 2006 22:05:22 - 25 Jul 2006 14:48:27 (2 days 16 hours 43 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

3 swarms found nearby.

2006

PS20060717.1(122.3km)

17 Jul

1 day 23 hours

64 earthquakes

PS20060717.2(16.2km)

17 Jul

4 hours

5 earthquakes

PS20060719.1(52.0km)

18 Jul

1 day 20 hours

10 earthquakes

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Seismic Swarm PS20060723.1: Analysis of Activity off West Java

An earthquake swarm designated PS20060723.1 occurred approximately 193 km south-southwest of Kawalu, Indonesia, between 22:05 UTC on 22 July 2006 and 14:48 UTC on 25 July 2006. Over 64 hours and 43 minutes, the sequence produced 17 events with magnitudes ranging from 4.8 to 5.3. The events clustered at depths between 10 km and 30 km, with several occurring at 10 km depth during the later stages.

The sequence began with a magnitude 5.3 event at 30 km depth. Subsequent activity on 23 July included magnitudes of 5.1, 4.8, 5.2, 5.0, and 5.0 at depths from 11 km to 30 km. On 24 July, six events registered magnitudes of 5.1, 5.1, 5.2, 5.0, 5.1, and 5.0, mostly at shallower depths around 10 km. The final day featured four events on 25 July, including two at magnitude 5.3 and 5.2, concluding the swarm.

This swarm represents the earliest recorded since 1 January 2000 in the regional catalog, with two additional swarms noted in later years. Such sequences are characterized by closely spaced events without a dominant mainshock, often linked to fluid migration or stress adjustments along fault networks.

The location lies within the Sunda subduction zone, where the Indo-Australian Plate converges with the Eurasian Plate at rates of approximately 6–7 cm per year. This tectonic setting generates frequent seismicity along the megathrust interface and overlying crustal faults south of Java. Depths recorded in the swarm align with upper-plate and intraslab activity typical of the region.

West Java has experienced recurrent moderate earthquakes due to this subduction dynamics, with historical events including the 2006 Yogyakarta earthquake and earlier tsunamigenic shocks. The swarm's offshore position places it near the trench slope, where extensional faults and accretionary prism structures can host clustered activity.

Seismic monitoring in Indonesia has improved since the early 2000s through expanded networks, allowing better resolution of swarm patterns. The 2006 sequence illustrates how moderate-magnitude clusters can occur without escalation, providing data on background stress release in the subduction forearc.

References

USGS Earthquake Catalog (events and regional tectonics).
Global CMT Project (focal mechanisms and plate motion data).
Indonesian Meteorological, Climatological, and Geophysical Agency (BMKG) annual seismicity reports.