7 research outputs found
Evaluating How Well Active Fault Mapping Predicts earthquake surface-rupture locations
Earthquake surface-fault rupture location uncertainty is a key factor in fault displacement hazard analysis and informs hazard and risk mitigation strategies. Geologists often predict future rupture locations from fault mapping based on the geomorphology interpreted from remote-sensing data sets. However, surface processes can obscure fault location, fault traces may be mapped in error, and a future rupture may not break every fault trace. We assessed how well geomorphology-based fault mapping predicted surface ruptures for seven earthquakes: 1983 M 6.9 Borah Peak, 2004 M 6.0 Parkfield, 2010 M 7.2 El MayorâCucapah, 2011 M 6.7 Fukushima-Hamadori, 2014 M 6.0 South Napa, 2016 M 7.8 Kaikoura, and 2016 M 7 Kumamoto. We trained geoscience students to produce active fault maps using topography and imagery acquired before the earthquakes. A geologic professional completed a âcontrolâ map. Mappers used a new âgeomorphic indicator rankingâ approach to rank fault confidence based on geomorphologic landforms. We determined the accuracy of the mapped faults by comparing the fault maps to published rupture maps. We defined predicted ruptures as ruptures near a fault (50â200 m, depending on the fault confidence) that interacted with the landscape in a similar way to the fault. The mapped faults predicted between 12% to 68% of the principal rupture length for the studied earthquakes. The median separation distances between predicted ruptures and strong, distinct, or weak faults were 15â30 m. Our work highlights that mapping future fault ruptures is an underappreciated challenge of fault displacement hazard analysisâeven for expertsâwith implications for risk management, engineering site assessments, and fault exclusion zones
Surface rupture of multiple crustal faults in the 2016 Mw 7.8 KaikĆura, New Zealand, earthquake
Multiple (>20
>20
) crustal faults ruptured to the ground surface and seafloor in the 14 November 2016 M w
Mw
7.8 KaikĆura earthquake, and many have been documented in detail, providing an opportunity to understand the factors controlling multifault ruptures, including the role of the subduction interface. We present a summary of the surface ruptures, as well as previous knowledge including paleoseismic data, and use these data and a 3D geological model to calculate cumulative geological moment magnitudes (M G w
MwG
) and seismic moments for comparison with those from geophysical datasets. The earthquake ruptured faults with a wide range of orientations, sense of movement, slip rates, and recurrence intervals, and crossed a tectonic domain boundary, the Hope fault. The maximum net surface displacement was âŒ12ââm
âŒ12ââm
on the Kekerengu and the Papatea faults, and average displacements for the major faults were 0.7â1.5 m south of the Hope fault, and 5.5â6.4 m to the north. M G w
MwG
using two different methods are M G w
MwG
7.7 +0.3 â0.2
7.7â0.2+0.3
and the seismic moment is 33%â67% of geophysical datasets. However, these are minimum values and a best estimate M G w
MwG
incorporating probable larger slip at depth, a 20 km seismogenic depth, and likely listric geometry is M G w
MwG
7.8±0.2
7.8±0.2
, suggests â€32%
â€32%
of the moment may be attributed to slip on the subduction interface and/or a midcrustal detachment. Likely factors contributing to multifault rupture in the KaikĆura earthquake include (1) the presence of the subduction interface, (2) physical linkages between faults, (3) rupture of geologically immature faults in the south, and (4) inherited geological structure. The estimated recurrence interval for the KaikĆura earthquake is â„5,000â10,000ââyrs
â„5,000â10,000ââyrs
, and so it is a relatively rare event. Nevertheless, these findings support the need for continued advances in seismic hazard modeling to ensure that they incorporate multifault ruptures that cross tectonic domain boundaries
Coseismic Rupture and Preliminary Slip Estimates for the Papatea Fault and Its Role in the 2016 Mw 7.8 KaikĆura, New Zealand, Earthquake
International audienceCoseismic rupture of the 19âkmâlong northâstriking and westâdipping sinistral reverse Papatea fault and nearby structures and uplift/translation of the Papatea block are two of the exceptional components of the 14 November 2016 Mw 7.8 KaikĆura earthquake. The dualâstranded Papatea fault, comprising main (sinistral reverse) and western (dipâslip) strands, ruptured onshore and offshore from south of Waipapa Bay to George Stream in the north, bounding the eastern side of the Papatea block. Fault rupture mapping was aided by the acquisition of multibeam bathymetry, light detection and ranging (lidar) topography and other imagery, as well as differential lidar (Dâlidar) from along the coast and Clarence River valley. On land, vertical throw and sinistral offset on the Papatea fault was assessed across an aperture of ±100ââm using uncorrected Dâlidar and field data to develop preliminary slip distributions. The maximum upâtoâtheâwest throw on the main strand is âŒ9.5±0.5ââmâ , and the mean throw across the Papatea fault is âŒ4.5±0.3ââmâ . The maximum sinistral offset, measured near the coast on the main strand, is âŒ6.1±0.5ââmâ . From these data, and considering fault dip, we calculate a maximum net slip of 11.5±2ââm and an average net slip of 6.4±0.2ââm for the Papatea fault surface rupture in 2016. Large sinistral reverse displacement on the Papatea fault is consistent with uplift and southward escape of the Papatea block as observed from Interferometric Synthetic Aperture Radar (InSAR) and optical image correlation datasets. The throw and net slip are exceedingly high for the length of the Papatea fault; such large movements likely only occur during multifault KaikĆuraâtype earthquakes that conceivably have recurrence times of â„5000â12,000ââyrsâ . The role of the Papatea fault in the KaikĆura earthquake has significant implications for characterizing complex fault sources in seismic hazard models
The Mw7.8 2016 Kaikoura earthquake: surface fault rupture and seismic hazard context
We provide a summary of the surface fault ruptures produced by the Mw7.8 14 November 2016 KaikĆura earthquake, including examples of damage to engineered structures, transportation networks and farming infrastructure produced by direct fault surface rupture displacement. We also provide an overview of the earthquake in the context of the earthquake source model and estimated ground motions from the current (2010) version of the National Seismic Hazard Model (NSHM) for New Zealand. A total of 21 faults ruptured along a c.180 km long zone during the earthquake, including some that were unknown prior to the event. The 2010 version of the NSHM had considered multi-fault ruptures in the KaikĆura area, but not to the degree observed in the earthquake. The number of faults involved a combination of known and unknown faults, a mix of complete and partial ruptures of the known faults, and the non-involvement of a major fault within the rupture zone (i.e. the Hope Fault) makes this rupture an unusually complex event by world standards. However, the strong ground motions of the earthquake are consistent with the high hazard of the KaikĆura area shown in maps produced from the NSHM
Surface Displacement Distributions for the July 2019 Ridgecrest, California, Earthquake Ruptures
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Documentation of surface fault rupture and ground-deformation features produced by the 4 and 5 July 2019 Mw6.4 and Mw7.1 ridgecrest earthquake sequence
The Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence occurred on 4 and 5 July 2019 within the eastern California shear zone of southern California. Both events produced extensive surface faulting and ground deformation within Indian Wells Valley and Searles Valley. In the weeks following the earthquakes, more than six dozen scientists from government, academia, and the private sector carefully documented the surface faulting and ground-deformation features. As of December 2019, we have compiled a total of more than 6000 ground observations; approximately 1500 of these simply note the presence or absence of fault rupture or ground failure, but the remainder include detailed descriptions and other documentation, including tens of thousands of photographs. More than 1100 of these observations also include quantitative field measurements of displacement sense and magnitude. These field observations were supplemented bymapping of fault rupture and ground-deformation features directly in the field as well as by interpreting the location and extent of surface faulting and ground deformation from optical imagery and geodetic image products. We identified greater than 68 km of fault rupture produced by both earthquakes aswell as numerous sites of ground deformation resulting from liquefaction or slope failure. These observations comprise a dataset that is fundamental to understanding the processes that controlled this earthquake sequence and for improving earthquake hazard estimates in the region. This article documents the types of data collected during postearthquake field investigations, the compilation effort, and the digital data products resulting from these efforts