USGS Earthquake Database Lists Only 21 Earthquakes Around Mt Axial Seamount

The USGS Earthquake Database allows regional searches within selected areas, permitting date range as early as 1926, and geometrical range by selected points on their (Mercator projection) Map, and earthquake magnitude max/min levels.
https://earthquake.usgs.gov/earthquakes/map/?extent=43.40505,-136.25244&extent=50.12762,-126.52954&range=search&sort=oldest&listOnlyShown=true&showUSFaults=true&baseLayer=terrain&search={"name":"Search%20Results","params":{"starttime":"1925-01-17%2000:00:00","endtime":"2025-01-24%2023:59:59","maxlatitude":49.739,"minlatitude":43.835,"maxlongitude":-127.991,"minlongitude":-134.714,"minmagnitude":-0.5,"maxmagnitude":9,"orderby":"magnitude"}}

When the region around the active underwater seamount Axial off of the Oregon Coast is searched, for date ranges as early as 1925, only 21 earthquakes are listed with 100 km of the seamount. Specific earthquakes are listed, several corresponding to the 1975, 1977, 1985, 1998, 2011 and 2015 eruptions, but none others.

  1. Since hundreds of additional earthquakes are known to have happened, does anyone know why earthquakes in this one particular region are not reported by the search program?
  2. Since the Axial Seamount is expected to resume eruptions soon, and since the Cascadia offshore Fault itself appears overdue for another of its periodic 8.3+ Mag earthquakes, who (at the USGS) can assign a regional watch to their earthquake mapping service website?

Select as Format : Magnitude, then you will see 1891 earthquakes listed.

Best

George Voulgaris, PhD
Program Director - OOI
GEO/OCE, www.nsf.gov
Tel 703 203 3824

Thank you for your quick reply. I do appreciate your efforts, particularly after hours over in DC.

The USGS EQ Database only includes earthquakes detected by seismometers on land. Those sensors only detect the largest events offshore, and the locations are poorly constrained. Since the early 1990’s coastal hydrophone arrays from the US Navy began to be used to detect and locate much smaller earthquakes in the NE Pacific. Then in late 2014, an ocean bottom seismometer network connected to the OOI Regional Cabled Array came online, and since then has been operated by researchers at University of Washington. Thousands of earthquakes have been detected, but again most are very small (not detected on land, and so are not part of the USGS database). One OOI-RCA earthquake catalog for Axial Seamount is displayed here:

http://axial.ocean.washington.edu/

I’m not sure what your 2nd question refers to, but the next eruption at Axial Seamount will not have any impact on the Cascadia subduction zone – it is too far away (just as the 1998, 2011, and 2015 eruptions had no impact). FYI, those are the only known dates of documented recent eruptions at Axial Seamount. There have certainly been earlier eruptions, but the exact dates are not known.

-Bill Chadwick

The USGS catalog is an earthquake catalog the covers the globe and combines both a global earthquake catalog created by the USGS and catalogs for various regional land-based seismic networks around the US all of which are based on land. The closest one of these is the Pacific Northwest Seismic network (PNSN). The PNSN is not very sensitive to small earthquakes well offshore (250 miles) and moreover Axial Seamount lies outside their designated area of coverage so they will not include its earthquakes in their catalog. I think the USGS catalog will only include earthquakes on Axial Seamount if they are big enough to make it into their global catalog which would typically require a magnitude (M) of at least 3.5. (I note they have an M2.6 from the 1998 eruption which may have been something they looked for when they learned of the eruption from SOSUS hydrophone monitoring)

Most of the earthquakes on Axial are M1 or smaller with a few up to ~M2 and only during eruptions might there be earthquakes bigger than M2 and even then only a few will be big enough for the USGS catalog. Because of the OOI cabled array we have various research catalogs. The first which we still keep running is mine at
http://axial.ocean.washington.edu/
and there is now a much more sophisticated one created by Felix Waldhauser and Kaiwen Wang at Columbia U
https://axialdd.ldeo.columbia.edu/

Regarding your second question, there are definitely a fair sized group of scientists keeping an eye on Axial Seamount as it moves towards an eruption because we can learn a lot about this volcano and volcanos in general from its eruptions. But they are not hazardous (except to our equipment) because they are a mile below the sea surface and are basaltic eruptions that are similar in vigor to eruptions in Hawaii. Eruptions at Axial are also not linked to elevated earthquake risk on the Cascadia Subduction Zone.

William Wilcock

Another thing of note is that the seismic networks have improved steadily from being quite limited before ~1970, to being much improved by the 1990s to being even better now so it is no surprise that there is nothing in the catalog before the mid 1970s

I only get 13 earthquakes that I might associate with Axial Seamount
https://earthquake.usgs.gov/earthquakes/map/?extent=44.71356,-130.7373&extent=46.99711,-127.90283&range=search&timeZone=utc&search=%7B%22name%22:%22Search%20Results%22,%22params%22:%7B%22starttime%22:%221900-01-01%2000:00:00%22,%22endtime%22:%222025-01-31%2023:59:59%22,%22maxlatitude%22:46.423,%22minlatitude%22:45.306,%22maxlongitude%22:-127.969,%22minlongitude%22:-130.671,%22minmagnitude%22:0.5,%22orderby%22:%22time%22%7D%7D

The last of those in 2019 is likely not on the Seamount because it locates 50 miles to the ESE (earlier events would tend to be poorly located so could be associated with the seamount). The 1977 and 1986 earthquakes are interesting. I believe there is some evidence for an eruption in 1986 but I was not aware of the M4.8 earthquake in 1977 which would be inline with the volcano erupting every ~10 years.