← Back to Axial Seamount Earthquake Catalog
by Maochuan Zhang
Page last updated: 12-Sep-2026 11:47:16 UTC
Continuous Amplitude Seismic Monitoring (CASM) — also known as Real-time Seismic Amplitude Measurement (RSAM) — tracks the median absolute amplitude of seismic waveforms at all seven OOI Axial Seamount stations in two frequency bands: 1–2 Hz and 2–4 Hz. Data are sourced from the always-available 8 Hz MHZ channel (SEED band code M, ~8 samples per second), providing uninterrupted monitoring independent of the 200 Hz broadband stream status.
Two figures are shown for each time window: the first shows station AXCC1 (Central Caldera) alone as a reference for caldera seismicity; the second combines the six outer stations — AXEC1, AXEC2, AXEC3, AXAS1, AXAS2, AXID1 — with one color per station and solid lines for 1–2 Hz, dashed lines for 2–4 Hz. Amplitudes are in raw counts (not normalized), so absolute levels are comparable across time.
Data resolution: 1 value per minute, updated hourly.
This page started operating online in March 2026.
Each time window shows two figures. The top figure shows AXCC1 (Central Caldera) with the 1–2 Hz band (blue) and 2–4 Hz band (red) overlaid. The bottom figure shows the six outer stations, each in a distinct color (solid = 1–2 Hz, dashed = 2–4 Hz).
Elevated amplitudes indicate increased seismic activity. Simultaneous increases in both bands and across multiple stations are characteristic of earthquake swarms. Comparing AXCC1 against the outer stations reveals whether activity is localized to the caldera or distributed across the rift zone.
Axial Seamount is one of the most seismically active volcanoes on Earth. Background seismicity is continuous, and episodic swarms — particularly in the caldera — can indicate magmatic activity or fault slip. The 2015 eruption was preceded by a sharp increase in CASM amplitude across caldera stations in the hours before the eruption onset.
OOI Cabled Array seafloor stations monitored: AXCC1 (Central Caldera), AXEC1, AXEC2, AXEC3 (East Caldera), AXAS1, AXAS2 (ASH), AXID1 (International District). All are broadband seismometers (OO network) on the Juan de Fuca Ridge at ~1500 m water depth. Data are recorded on the 8 Hz MHZ channel.
The RSAM/CASM method was introduced by:
Endo, E. T., and Murray, T. L. (1991). Real-time Seismic Amplitude Measurement (RSAM): a volcano monitoring tool. Bulletin of Volcanology, 53, 533–545. https://doi.org/10.1007/BF00298154
When using earthquake catalog data from this site, please cite:
Wilcock, W. S. D., M. Tolstoy, F. Waldhauser, C. Garcia, Y. J. Tan, D. R. Bohnenstiehl, J. Caplan-Auerbach, R. P. Dziak, A. Arnulf, & M. E. Mann (2016). Seismic constraints on caldera dynamics from the 2015 Axial Seamount eruption. Science, 354, 1395–1399.