Shallow geometry and displacements on the San Andreas Fault near Point Arena based on trenching and 3‐D georadar surveying

Gross, Ralf; Green, Alan; Holliger, Klaus; Horstmeyer, Heinrich; Baldwin, John N.

doi:10.1029/2002gl015534

Cited by 27 publications

(18 citation statements)

References 11 publications

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“…Gross et al 2000Gross et al , 2002Gross et al , 2003Gross et al , 2004Tronicke et al 2004;McClymont et al 2008aMcClymont et al , b, 2010, pseudo-3-D GPR (combined with a few CMP acquisitions) is an appropriate tool to investigate the subsurface and discriminate the various sedimentary and deformation features that it contains, down to a resolution of a few tens of centimetres. McCalpin 2009), it has not been applied so far on a scale larger than palaeoseismological trenches.…”

Section: O N C L U S I O N Smentioning

confidence: 99%

Finding the buried record of past earthquakes with GPR-based palaeoseismology: a case study on the Hope fault, New Zealand

Beauprêtre¹,

Garambois²,

Manighetti³

et al. 2012

Geophysical Journal International

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International audienceIn places where sedimentation and erosion compete at fast rates, part of the record of past earthquakes on faults may be buried, hence hidden, in the first few metres below the surface. We developed a novel form of palaeoseismology, of geophysical type, based on the use of a dense pseudo-3-D Ground Penetrating Radar (GPR) survey to investigate such possible buried earthquake traces, on a long, fast-slipping strike-slip fault (Hope fault, New Zealand), at a site (Terako) where marked alluvial conditions prevail. We first used LiDAR data to analyse the ground surface morphology of the 2 km2 site at the greatest resolution. Nineteen morphological markers were observed, mainly alluvial terrace risers and small stream channels that are all dextrally offset by the fault by amounts ranging between 3 and 200 m. The measurements document about 10 past earthquake slip events with a mean coseismic slip of 3.3 +/- 1 m, with the most recent earthquake event having a slip of 3 +/- 0.5 m. We then investigated a detailed area of the site (400 x 600 m2) with pseudo-3-D GPR. We measured 56, similar to 400 m long, 510 m spaced GPR profiles (250 MHz), parallel to the fault and evenly distributed on either side. The analysis revealed the existence of a palaeosurface buried at about 3 m depth, corresponding to the top of alluvial terraces of different ages. That buried surface is incised by a dense network of stream channels that are all dextrally offset by the fault. We measured 48 lateral offsets in the buried channel network, more than twice than at the surface. These offsets range between 6 and 108 m, as observed at the surface, yet provide a more continuous record of the fault slip. The similarity of the successive slip increments suggests a slip per event averaging 4.4 +/- 1 m, fairly similar to that estimated from surface data. From the total surface and buried 67 offset collection, we infer that a minimum of 30 large earthquakes have broken the Hope fault at the Terako site in the last about 67 kyr, with an average coseismic slip of 3.2 +/- 1 m, a minimum average recurrence time of about 200 yr, and a magnitude of at least Mw 7.07.4. Our study therefore confirms that part of the record of past earthquakes may indeed reside in the first few metres below the surface, where it may be explored with geophysical, GPR-based palaeoseismology. Developing such a new palaeoseismological tool should provide rich information that may complement surface observations and help to document the past earthquakes on faults

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Section: O N C L U S I O N Smentioning

confidence: 99%

Finding the buried record of past earthquakes with GPR-based palaeoseismology: a case study on the Hope fault, New Zealand

Beauprêtre¹,

Garambois²,

Manighetti³

et al. 2012

Geophysical Journal International

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“…In contrast to the rather limited success of 2‐D georadar profiling, migrated 3‐D georadar data recorded across the San Andreas Fault in Northern California provided detailed new knowledge of two active fault strands and yielded critical new information on coseismic movements along one of the strands [ Gross et al , 2002; Green et al , 2003]. The acquisition and processing strategies designed for our study of the San Andreas Fault [ Gross et al , 2003] were adopted for our investigations of the Wellington Fault.…”

Section: Previous Georadar Surveys Across Tectonically Active Faultsmentioning

confidence: 99%

Location and geometry of the Wellington Fault (New Zealand) defined by detailed three‐dimensional georadar data

et al. 2004

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[1] Earthquakes with surface-wave magnitudes of 7.3-7.9 are estimated to be associated with the rupture of the Wellington Fault at relatively regular intervals of 500-770 years. The last such earthquake probably happened between AD 1510 and 1660. Along its southern segment, the Wellington Fault passes through Wellington, New Zealand's capital, and the densely populated Hutt Valley. It is considered to be a highly hazardous structure. To map the shallow geometry of the Wellington Fault, we have collected 3-D groundpenetrating radar (georadar) data at two sites along the fault in the Hutt Valley. At one site, the first ever georadar fault plane reflections from an active strike-slip fault are observed. They coincide with conspicuous diffractions generated by abrupt truncations of structures against the fault plane. These georadar data provide the most vivid shallow images of any active fault surveyed to date. At the second site, apparent offsets of lineaments in the sedimentary sections on either side of the fault are consistent with $20 m of dextral displacement estimated from the offset of a nearby terrace riser. The dips and minimum depth extents of the primary zones of fault displacement at the two sites are 55-75°SE and $20 m and 72-84°SE and $12 m, respectively. Although the georadardefined zones of faulting are a few meters wide, prominent reflection fabrics suggest that shearing, fracturing, and crushing extend for several tens of meters on either side of the fault.

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“…Once the geographic locations of the faults and folds have been defined by the magnetic and electromagnetic data, high-resolution seismic and GPR surveys could then be targeted at critical locations. We suggest that 3D GPR techniques of the type successfully used to investigate active faults elsewhere (Gross et al, 2002(Gross et al, , 2004MyClymont et al, 2008aMyClymont et al, ,b, 2009aMyClymont et al, ,b, 2010 should be employed in future Canterbury Plains surveys.…”

Section: Conclusion and Recommendationsmentioning

confidence: 95%

Recent deformation of Quaternary sediments as inferred from GPR images and shallow P-wave velocity tomograms: Northwest Canterbury Plains, New Zealand

Carpentier

Green

Doetsch

et al. 2012

Journal of Applied Geophysics

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Shallow geometry and displacements on the San Andreas Fault near Point Arena based on trenching and 3‐D georadar surveying

Cited by 27 publications

References 11 publications

Finding the buried record of past earthquakes with GPR-based palaeoseismology: a case study on the Hope fault, New Zealand

Finding the buried record of past earthquakes with GPR-based palaeoseismology: a case study on the Hope fault, New Zealand

Location and geometry of the Wellington Fault (New Zealand) defined by detailed three‐dimensional georadar data

Recent deformation of Quaternary sediments as inferred from GPR images and shallow P-wave velocity tomograms: Northwest Canterbury Plains, New Zealand

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