Seismic Swarm PS20141009.1: Activity on the Southern East Pacific Rise

The southern East Pacific Rise (EPR) forms a fast-spreading segment of the global mid-ocean ridge system, marking the divergent boundary between the Pacific and Nazca plates. Spreading rates here reach 140–150 mm per year, driving frequent magmatic intrusions, hydrothermal venting, and shallow seismicity. The ridge axis lies at depths of approximately 2,500–3,000 m, with a narrow axial valley and robust volcanic construction typical of intermediate-to-fast spreading centers.

Seismic swarm PS20141009.1 occurred along this ridge segment beginning at 02:14 UTC on 9 October 2014 and concluding at 18:59 UTC on 10 October 2014. Over 40 hours and 44 minutes, ten earthquakes were recorded. Magnitudes ranged from 4.8 to 7.0, with focal depths between 10 and 33 km. The sequence opened with a magnitude-7.0 event at 16 km depth, followed within minutes by two events exceeding magnitude 6.5. Subsequent activity included several magnitude-5 events clustered near 10 km depth.

This pattern aligns with known EPR behavior, where swarms often reflect dike propagation or sudden slip along transform faults adjacent to the ridge axis. The largest event of the swarm (M 7.0) remains the strongest recorded on the southern EPR since 2000. Its epicenter lay approximately 31 km from the swarm centroid, suggesting the mainshock may have triggered or coincided with distributed faulting and minor magmatic movement along the ridge.

No damage or tsunami impacts were reported, consistent with the remote, deep-ocean setting. Historical monitoring of the EPR since the 1990s has documented similar short-duration swarms lasting one to three days, frequently accompanied by seafloor deformation detected by ocean-bottom instruments.

The 2014 swarm underscores the dynamic nature of fast-spreading ridges, where tectonic and volcanic processes operate on short timescales. Continued seismic and geodetic surveillance of the southern EPR remains essential for understanding crustal accretion and hazard potential along this remote plate boundary.

References

USGS Earthquake Catalog (events since 2000)
National Oceanic and Atmospheric Administration (NOAA) mid-ocean ridge bathymetry
Scientific literature on East Pacific Rise tectonics (e.g., Carbotte et al., 2012; Langmuir et al., 2018 updates)