A decade of horizontal deformation from great earthquakes

Abstract

The 21st Century has seen the occurrence of 17 great earthquakes (Mw >8), including some of the largest earthquakes ever recorded. Numerical modeling of the earthquakes shows that nearly half of the Earth's surface has undergone horizontal coseismic deformation >1 mm, with the 2004 Sumatra‐Andaman earthquake dominating the global deformation field. This has important implications for both the realization of a terrestrial reference frame and in the interpretation of regional tectonic studies based on GPS velocities. We show that far‐field coseismic deformations from great earthquakes will, if unaccounted for, introduce errors in estimates of linear site velocities of at least 0.1‐0.3 mm/yr across most of the surface of the Earth. The accumulated global deformation field shows that two regions, Australia and the north Atlantic/Arctic Ocean, have been largely undeformed by these great earthquakes, with accumulated deformations generally <0.5 mm. Using GPS estimates of surface deformation, we show that the majority of the Australian continent is deforming at <0.2 mm/yr, the northern part of New Zealand is rotating clockwise relative to the Australian Plate with relative horizontal velocities of ∼2 mm/yr, while the southeastern coast of Australia is undergoing post‐seismic relaxation caused by the 2004 Mw = 8.1 Macquarie Ridge earthquake. The presence of ongoing post‐seismic relaxation thousands of kilometers from plate margins violates the secular/linear assumption made in current terrestrial reference frame definitions. These effects have significant ramifications for regional tectonic interpretations and global studies such as sea level rise that require reference frame accuracy greater than this level.

The Samothrace Earthquake of May 2014 and the Displacements Estimations Using Permanent GPS Stations Data

“…A strong EQ have an effect on the time series analysis causing some discontinuities as offsets, which may lead to an unrealistic estimation of geodetic velocities (Bitharis et al, 2015). More generally (Tregoning et al, 2013) showed that large EQs can induce linear velocity errors of up to 0.4 mm/yr at sites over 1000 km from the earthquake locations. In Figure 2, daily displacements expressed in the topocentric (North, East, Up) system are presented for 018B (Samothrace Island) and LEMN (Lemnos Island) stations, which are the two nearest to the EQ epicentre.…”

Estimation of offsets in GPS time-series and application to the detection of earthquake deformation in the far-field

“…SAMP) as this work focuses only on stations in the far-field of an event. Following the studies of Watson et al (2010) and Tregoning et al (2013), we also discard the GPS stations which were strongly offset by the Macquarie Ridge earthquake (2004 December 23) which had a magnitude equal to M w 8 (e.g. AUCK, DUNT,CHAT,MAC1,HOB2,TIDB and MOBS).…”

“…The parameters to model the SumatraAndaman earthquake are exactly the same as the values of Pollitz et al (2006). The estimated values are the same as in Tregoning et al (2013) and displayed in Appendix C.…”

“…For the Sumatra-Andaman earthquake (M w > 9.0), the earthquake ruptured about 1300 km of the Sunda and Andaman subduction zone (Pollitz et al 2006;Banerjee et al 2007). Banerjee et al (2007) showed that GPS stations close to the ruptured subduction zone underwent vigorous post-seismic relaxation in the years following this event, while Watson et al (2010) and Tregoning et al (2013) showed post-seismic relaxation effects in South Australia following the December 2004 Macquarie Ridge earthquake. Thus, the estimation of a discontinuity in a GPS timeseries is more complicated when caused by an earthquake than in the case of an equipment change because of the possible presence of post-seismic non-linear signals, even thousands of kilometres from the earthquake rupture.…”

“…Events with magnitude M w > 9.0, create displacements over a large part (or all) of the globe. Previous studies, for example and Tregoning et al (2013), estimated millimetre-level coseismic offsets at GPS stations thousands of kilometres from earthquake ruptures. For the Sumatra-Andaman earthquake (M w > 9.0), the earthquake ruptured about 1300 km of the Sunda and Andaman subduction zone (Pollitz et al 2006;Banerjee et al 2007).…”