EarthScope Webinar - Thursday (5/30) @ 2p ET - A Multi-Decadal Analysis of the Global Microseism and Ocean Wave Climate

[Justin Sweet]

Please register for the next EarthScope Webinar happening Thursday, May 30th at 2PM Eastern 

Title: A Multi-Decadal Analysis of the Global Microseism and Ocean Wave Climate

Presenter: Dr. Rick Aster, Colorado State University

Register in advance for this webinar: https://earthscope-org.zoom.us/webinar/register/WN_S3uKzwVOTTyjCbv-qsomxw

After registering, you will receive a confirmation email containing information about joining the webinar. 

Abstract: 

It has been recognized since the dawn of global seismology that the oceans produce a continuous and seasonally varying microseism signal that is detectable everywhere on Earth.  Standardized global digital seismographic networks such as the Global Seismographic Network (GSN) and GEOSCOPE now facilitate the uniform analysis of microseism energy across nearly four decades spanning recently accelerating anthropogenic climate change. The globally observable primary microseism signal near 20–14 s period is a particularly apt proxy for global near-coastal wave energy because it is produced by propagating ocean wave seafloor tractions applied at depths of less than about 300 meters and is less sensitive to wave and bathymetric conditions than the more energetic and widely studied secondary microseism signal.

Examining continuous digital vertical component seismic records (principally sensing large-scale Rayleigh waves) beginning in the late 1980s, a robust secular trend estimation procedure reveals highly significant and geographically correlated increasing primary microseism amplitudes and energies at 41 of 52 long-running GSN stations. The greatest absolute rates of increase are observed for station PMSA on the Antarctic Peninsula with seismic (acceleration) amplitude and (velocity-squared) energy trends through August 2022 (±3σ confidence intervals) of 0.037±0.008 nm/s2/y (0.36±0.08 %/y relative to the long-term station median) and 4.16±1.07 (nm/s)2/y (0.58±0.15 %/y), respectively. Assuming linearity and constant ocean wave-seismic wave coupling, the corresponding inferred rate of global near-coastal ocean wave energy increase is 0.27±0.03 %/y for the full record and 0.35±0.04 %/y for the record from the turn of the 21st century. 

These inferred rates of ocean wave intensification compare well with independent estimates from oceanographic and meteorological data. Time-smoothed (e.g. 2-month) primary microseism signal station histories regionally cluster to thousands of kilometers of geographic separation, demonstrating large-scale and consistent sampling of ocean wave forces.  Multi-year primary microseism signal variations also correlate well with El Niño and La Niña conditions that affect large-scale storm energy in the Pacific region, with increasing energy in the southwest Pacific under positive El Niño-Southern Oscillation (ENSO) conditions and in the southeast Pacific under negative ENSO (positive Southern Oscillation; SOI) climate index conditions.

Similar analysis of the 5–12 s period secondary microseism signal shows generally consistent but more variable temporal and geographic trends attributable to the more specific ocean depth and wave-wave interference conditions necessary for its excitation.  Primary and secondary histories additionally show station-specific seasonal phase and amplitude relationships that reflect seasonal ocean wave variability and provide further insight into ocean wave state.  

All EarthScope webinars are archived for later viewing at 

https://www.youtube.com/playlist?list=PLGQwSTwiUcKwWZ9lhS2shpwMPwKSNl3Eo

	Justin Sweet, PhD
	Project Manager

justin...@earthscope.org