Data Event Response to the October 30, 2020 M 7.0 - 15 km NNE of Néon Karlovásion, Greece Earthquake

Written by Shelley Olds & Kathleen Hodgkinson
Originally posted 17 November 2020

Event Summary

A magnitude 7.0 earthquake occurred at 2020-10-30 11:51:27 (UTC) on October 30, 2020, off the coast of Greece and Turkey. For more information, see the USGS Earthquake Hazards Program event page

The event occurred ~350 km south of a borehole strainmeter network installed by UNAVCO for the GONAF project and operated as part of the Network of the Americas (NOTA) project. NOTA is a core component of the NSF Geodetic Facility for the Advancement of Geoscience (GAGE), operated by UNAVCO.

GAGE Response

GONAF Borehole Strainmeter Data
UNAVCO has produced a fully processed 1-sps borehole strainmeter (BSM) dataset from the strainmeters in Turkey for this event. This dataset can be downloaded from the UNAVCO borehole strainmeter event response page.

Between 2014 and 2016 UNAVCO installed six borehole strainmeters as part of the geodetic component of the Geophysical Observatory to study the North Anatolian Fault project (GONAF). The strainmeters are of the same design as those deployed for the EarthScope Plate Boundary Observatory program (Gladwin Tensor Strainmeters). Installed at depths of up to a hundred meters, they consist of four independent horizontal gauges. Measurements are made in four directions and when combined can reveal changes in areal and shear strain as small as 1 picostrain (10^-12).

GONAF is a collaborative effort between the Turkish Disaster and Emergency Management Presidency (AFAD), Kandilli Observatory, the Earthquake Research Institute at Bogazici University, the University of Colorado, Boulder, the German Research Centre for Geosciences (GFZ), and the National Science Foundation. A goal of the project is to detect creep events on the segments of the North Anatolian Fault that lie below the Marmara Sea. These sections, which have been identified as a seismic gap, lie to the south and southeast of Istanbul, a city of 20 million people. In the summer of 2016 one of the GONAF strainmeters, (ESN1) recorded a 2-month long ultra-slow earthquake in (Martínez-Garzón et al., 2018).

Work lead by Andy Barbour at the USGS has shown that strainmeters can also play an important role in Earthquake Early Warning programs (Barbour and Crowell, 2017; Farghal, Barbour and Langbein, 2020). Using NOTA strainmeters installed in the United States, Barbour and his co-authors derived an empirical equation relating peak dynamic strain, earthquake moment magnitude, and hypocentral distance. The benefit strainmeters provide over traditional seismic-based networks is that the magnitude estimate does not saturate at ~M7.

Using the empirical relation derived by Barbour’s team the GONAF strainmeters indicated within ~105 seconds of the origin time that this earthquake was ~M7 (see Figure 3). The time taken to provide an estimate of the magnitude is largely a function of the distance of the strainmeters from the event epicenter, in this case several hundred kilometers. For an explanation of these plots, see our UNAVCO Geophysical Event Response Data Explainer: Dynamic Strain.

References

• Barbour, A. J., and B. W. Crowell (2017), Dynamic Strains for Earthquakes Source Characterization, Seismological Research Letters, 88(2A), 354 — 370, DOI: 10.1785/0220160155
• Bird, P., (2003), An updated digital model of plate boundaries, Geochem. Geophys. Geosyst., 4(3), 1027, DOI:10.1029/2001GC000252
• Farghal, N. S., Barbour, A. J., and J. O. Langbein (2020), The Potential of Using Dynamic Strains in Earthquake Early Warning Applications, Seismological Research Letters, 91(5), 2817-2827, DOI: 10.1785/0220190385
• Martinez Garzon, P., Bohnhoff, M., Mencin, D., Kwiatek, G., Dresen, G., Hodgkinson, K., Nurlu, M., Kadirioglu, F. T., Kartal, R. F. (2019): Slow strain release along the eastern Marmara region offshore Istanbul in conjunction with enhanced local seismic moment release. Earth and Planetary Science Letters, 510, 209-218. DOI: https://doi.org/10.1016/j.epsl.2019.01.001

Note: Figures and findings are preliminary and subject to revision.