Predictions of Martian Volcano-tectonic Seismicity from Extrapolation of
48 Years of Hawai'ian Earthquakes.
Abstract
The NASA InSight mission, landing in late November 2018, promises to
revolutionize our understanding of Martian interior structure via
analysis of seismic data returned by the SEIS instrument. The extent to
which the mission’s potential is realized will depend on the number of
detectable seismic events that occur during the period of operation.
Here I estimate the rate of detectable events generated by
volcano-tectonic activity on Mars based on extrapolation of Hawai’i’s
seismic record. I use a catalog of 5603 earthquakes spanning 48 years
[IRIS, 2018], with moment magnitudes MW ranging from 3.0 to 6.9, to
derive the Gutenberg-Richter (G-R) frequency-magnitude relation for the
Island of Hawai’i, expressed as log(N) = a – b MW, where N is the
number of earthquakes with magnitudes greater than or equal to MW, and a
and b are constants. By this analysis, one earthquake with MW 5.1 or
greater can be expected every year at Hawai’i. Under the assumption that
the mechanisms of seismicity associated with edifice building are
similar at Hawai’i and Olympus Mons (supported by observation of
decollement-based volcanic spreading at both), I use the same b for both
settings and scale a according to estimates of magmatic volume flux
rates dV/dt at both settings. Over the 80 Myr history of the
Hawaiian-Emperor volcanic chain, dV/dt ≈ 1.7 x 10-2 km3/yr. An estimate
of dV/dt for the Olympus Mons volcano on Mars was derived from
paleotopographic analysis of a set of lava flows south of Olympus Mons
with discordant topography. Given the mean flow age from crater counts
(210 Ma), an estimate of the amount of volcanic material needed to cause
deflections of flow orientations of the required magnitudes yields
estimates of dV/dt over this timespan ranging from 6.33 x 10-4 to 6.43 x
10-3 km3/s. Taking the mean of these values and scaling a by the ratio
of dV/dt values for Mars and Hawai’i yields a rate of at least 1 quake
of MW = 4.4 or greater per year (Figure 1). Thus, under several
assumptions (including a steady recent magma supply rate for Olympus
Mons), we can expect ≈ 2 volcano-tectonically driven quakes of magnitude
MW > 4.4 from the vicinity of Olympus Mons during the
nominal 2 Earth-year InSight prime mission. This is a conservative lower
bound that does not consider contributions from numerous potential
volcano-tectonic sources in Tharsis and elsewhere on Mars.