8.5+Yr of Persistent Intraplate Seismicity Beneath Santiago City, Chile

Understanding the occurrence and persistence of intraplate seismicity is essential for improving earthquake source models and refining seismic hazard assessments, particularly when such activity develops beneath densely populated regions. Central Chile is globally recognized for its large megathrust earthquakes, but crustal seismicity within the overriding South American plate remains poorly characterized. One notable example is the Santa Rosa cluster, a localized source of seismicity located ∼20–30 km beneath southern Santiago, where more than seven million people live. In this work, we analyze ∼8.5 yr (2017–2025) of continuous seismic data using a single-station matched-filter approach to better characterize the spatiotemporal evolution of this cluster. Our method increases the number of detected events by more than an order of magnitude relative to previous catalogs, yielding 1389 earthquakes organized into families of
highly similar waveforms. The seismicity is confined to a compact lower-crustal volume and exhibits episodic bursts separated by quiescent intervals, with no evidence of long-term decay. Two distinct subclusters are identified: the southern one dominates seismic moment release and shows a recent increase in event size, whereas the northern one remains less productive. These observations suggest that local variations in stress
and/or fluid pressure modulate the asynchronous activity of the subclusters and sustain their long-term persistence. Although magnitudes remain small (generally M < 3), the stability of this source over multiple decades indicates a long-lived intraplate process occurring directly beneath Chile’s most populated region. Our findings highlight the need for denser seismic monitoring to better constrain the physical mechanisms controlling this activity and to improve assessments of intraplate seismic hazard in central Chile.