Earthquake nucleation and fault slip complexity in the lower crust of central Alaska
(pdf, supplement, report)
Nature Geoscience, 2018
Carl Tape, Stephen Holtkamp, Vipul Silwal, Jessica Hawthorne, Yoshihiro Kaneko, Chen Ji, Natalia Ruppert, Kyle Smit, Michael E. West
Earthquakes start under conditions that are largely unknown. In laboratory analogue experiments and continuum models, earthquakes transition from slow-slipping, growing nucleation to fast-slipping rupture. In nature, earthquakes generally start abruptly, with no evidence for a nucleation process. Here we report evidence from a strike-slip fault zone in central Alaska of extended earthquake nucleation and of very-low-frequency earthquakes (VLFEs), a phenomenon previously reported only in subduction zone environments. In 2016, a VLFE transitioned into an earthquake of magnitude 3.7 and was preceded by a 12-hour-long accelerating foreshock sequence. Benefiting from 12 seismic stations deployed within 30 km of the epicenter, we identify coincident radiation of distinct high-frequency and low-frequency waves during 22 s of nucleation. The power-law temporal growth of the nucleation signal is quantitatively predicted by a model in which high-frequency waves are radiated from the vicinity of an expanding slow slip front. The observations reveal the continuity and complexity of slip processes near the bottom of the seismogenic zone of a strike-slip fault system in central Alaska.
This material is based upon work supported by the National Science Foundation under Grant Number EAR-1352668.
Minto Flats fault zone of central Alaska. (a) Beachballs represent source mechanisms for earthquakes (EQ) and very-low-frequency earthquakes (VLFE) discussed in this study (Tab. S1). From north to south, these are: 1995-10-06 Mw 6.0 EQ (18 km), 2015-09-12 Mw 3.8 VLFE (21 km), 2012-04-11 Mw 3.8 VLFE+EQ (16 km), 2015-10-22 Mw 2.6 EQ (18 km), 2013-03-12Mw 3.5 VLFE (23 km), 2016-01-14Mw 3.7 VLFE+EQ (17 km), 2015-10-31 Mw 3.4 EQ (25 km). The thick black lines denote the two left-lateral faults of the Minto Flats fault zone. Inverted triangles denote seismic stations, with MDM at far right. (b) Envelopes of high-frequency seismograms at station MDM for five events in (a). For a typical earthquake (top), there is no high-frequency foreshock (HFF) signal prior to the P wave of the earthquake. Other events show an increasing signal that is associated with nucleation and VLFEs. The arrows labeled VLFE indicate the onset time of low-frequency waves such as those shown in Figure 2a. [Tape et al., 2018]
Press coverage and related articles
Press coverage and related articles
Earthquake nucleation and fault slip complexity in the lower crust of central AlaskaTape, Holtkamp, Silwal, Hawthorne, Kaneko, Ampuero, Ji, Ruppert, Smith, WestNature Geoscience (2018)https://rdcu.be/SOThwebpage: https://www.nature.com/articles/s41561-018-0144-2
Nucleation of the 1999 Izmit earthquake by a triggered cascade of foreshocksEllsworth and BulutNature Geoscience (2018)https://rdcu.be/SOQCwebpage: https://www.nature.com/articles/s41561-018-0145-1
Unsettled earthquake nucleationJoan Gomberg (2018)Nature Geoscience (2018)https://rdcu.be/SONowebpage: https://www.nature.com/articles/s41561-018-0149-x
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UAF press release:https://news.uaf.edu/scientists-find-pre-earthquake-activity-in-central-alaska/
GNS media release:https://www.gns.cri.nz/Home/News-and-Events/Media-Releases/Deep-signals-may-hold-clues-for-understanding-how-quakes-start-05-06-2018
Fairbanks Daily News-Minerhttp://www.newsminer.com/news/local_news/university-of-alaska-fairbanks-examines-quake-prediction-method/article_5875ff74-6889-11e8-9695-db6575ab9728.html
KUAC radio interview by Dan Bross (starts at 4:30)http://fm.kuac.org/post/06-06-18-kuac-morning-news
NBC 11http://www.webcenter11.com/content/news/University-scientists-make-new-earthquake-discoveries-485023531.html
Anchorage Daily Newshttps://www.adn.com/alaska-news/science/2018/06/05/tantalizing-clues-could-lead-to-earthquake-forecasts-uaf-researchers-say/
Seattle Timeshttps://www.seattletimes.com/nation-world/alaska-researchers-examine-low-frequency-earthquakes/
US News and World Reporthttps://www.usnews.com/news/best-states/alaska/articles/2018-06-06/alaska-researchers-examine-low-frequency-earthquakes
Alaska Earthquake Centerhttps://earthquake.alaska.edu/when-earthquake-about-happen-foreshocks-earthquake-nucleation-and-earthquake-predictionforecasting
Fairbanks Daily News-Miner, June 5, 2018, showing a photo of PhD student Kyle Smith taken during installation of a T120PH sensor at station F6TP in September 2015. (Despite the headline, our Nature Geoscience article does not discuss earthquake prediction.)