Partitioned Off‐Fault Deformation in the 2016 Norcia Earthquake Captured by Differential Terrestrial Laser Scanning. Issue 6 (25th March 2019)

• Record Type: Journal Article
• Authors: Wedmore, L. N. J.; Gregory, L. C.; McCaffrey, K. J. W.; Goodall, H.; Walters, R. J.
• Is Part Of: Geophysical research letters. Volume 46:Issue 6(2019)
• Page Start: 3199
• Page End: 3205
• Publication Date: 2019-03-25
• Subjects: off‐fault deformation -- earthquake -- terrestrial laser scanning -- 2016 Central Italy earthquake -- shallow slip deficit; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2018GL080858
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Field measurements of coseismic fault slip often differ from surface slip models derived from satellite geodesy. Quantifying these differences is challenging as many geodetic techniques inadequately image near‐fault deformation. We use an iterative closest point algorithm to difference preearthquake and postearthquake terrestrial laser scanning point clouds to reveal centimeter‐scale patterns of surface deformation caused by shallow fault slip in the 2016 Mw 6.6 Norcia (Central Italy) earthquake. Terrestrial laser scanning offsets are constant along the fault and match average field measurements. Eighty‐four percent of vertical displacement occurs on a discrete fault zone, with 16% of deformation distributed across a narrow zone <4 m wide. In contrast, horizontal deformation is distributed over an 8‐m‐wide zone with approximately 50% of extension accommodated as off‐fault deformation (OFD). The centimeter‐scale observation of deformation shows that horizontal and vertical coseismic OFD is partitioned—in this case, OFD is dominated by horizontal deformation. Plain Language Summary: During an earthquake, slip on a fault plane creates discrete offsets at depth and at the surface. The pattern and size of offsets at the surface can help to understand what happened in the earthquake and also leaves a record of each event in the landscape. This record is used to infer past earthquake activity and forecast the potential likelihood of future earthquakes. We captured a preearthquake image of a fault that caused the 2016 magnitude 6.6 Norcia earthquake in Central Italy. By reimaging the same fault after the earthquake, we measured the pattern of ground movement during the event to millimeter precision to understand in unprecedented detail how much earthquake slip occurs on the fault itself. This uniquely precise map of surface deformation has never been captured before using a terrestrial laser scanner. We find that the vertical motion of the fault is mainly focused on the fault itself. In contrast, the horizontal motion is distributed over an 8‐m‐wide zone, with approximately 50% of the movement occurring away from the fault—known as off ‐ fault deformation . Our results have implications for how evidence of past earthquakes preserved in the landscape are interpreted for forecasting future seismic hazard. Key Points: The first known example of an earthquake rupture imaged with preearthquake and postearthquake terrestrial laser scanning We differenced the laser scans using an iterative closest point algorithm refined for accurately resolving centimeter‐scale offsets We find that off‐fault deformation is strongly partitioned between the horizontal and vertical components of displacement