Imaging the Plate Interface in the Cascadia Seismogenic Zone: New Constraints from Offshore Receiver Functions

Janiszewski, H. A.; Abers, G. A.

doi:10.1785/0220150104

Cited by 56 publications

(66 citation statements)

References 42 publications

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“…Receiver function analysis using data from ocean bottom seismometers (OBS) from the Cascadia Initiative (Toomey et al, 2014) may be able to provide constraints on material properties and/or pore-fluid pressure around the (offshore) megathrust by tracing the up-dip extent of the low-velocity zone in Cascadia (Audet, 2015;Janiszewski and Abers, 2015).…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

2016

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More than a decade after the discovery of deep episodic slow slip and tremor, or slow earthquakes, at subduction zones, much research has been carried out to investigate the structural and seismic properties of the environment in which they occur. Slow earthquakes generally occur on the megathrust fault some distance downdip of the great earthquake seismogenic zone in the vicinity of the mantle wedge corner, where three major structural elements are in contact: the subducting oceanic crust, the overriding forearc crust and the continental mantle. In this region, thermo-petrological models predict significant fluid production from the dehydrating oceanic crust and mantle due to prograde metamorphic reactions, and their consumption by hydrating the mantle wedge. These fluids are expected to affect the dynamic stability of the megathrust fault and enable slow slip by increasing pore-fluid pressure and/or reducing friction in fault gouges.Resolving the fine-scale structure of the deep megathrust fault and the in situ distribution of fluids where slow earthquakes occur is challenging, and most advances have been made using A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTteleseismic scattering techniques (e.g., receiver functions). In this paper we review the teleseismic structure of six well-studied subduction zones (three hot, i.e., Cascadia, southwest Japan, central Mexico, and three cool, i.e., Costa Rica, Alaska, and Hikurangi) that exhibit slow earthquake processes and discuss the evidence of structural and geological controls on the slow earthquake behavior. We conclude that changes in the mechanical properties of geological materials downdip of the seismogenic zone play a dominant role in controlling slow earthquake behavior, and that near-lithostatic pore-fluid pressures near the megathrust fault may be a necessary but insufficient condition for their occurrence.

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Section: Accepted M Manuscriptmentioning

confidence: 99%

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

2016

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“…There is much hope that similar outcomes may be achieved from the application of teleseismic scattering principles to the oceanic crust using OBS data (e.g. Janiszewski & Abers, 2015). Knowledge of the seismic properties of the oceanic crust as it evolves from the ridge to the trench are particularly important to validate current models of subduction zone structures that rely on the correspondence between the downgoing low-velocity zone with the subducting oceanic crust and delineate the onset of inferred high pore-fluid pressure region around the locked megathrust fault (Audet et al, 2009;Abers et al, 2009;Janiszewski & Abers, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…Janiszewski & Abers, 2015). Knowledge of the seismic properties of the oceanic crust as it evolves from the ridge to the trench are particularly important to validate current models of subduction zone structures that rely on the correspondence between the downgoing low-velocity zone with the subducting oceanic crust and delineate the onset of inferred high pore-fluid pressure region around the locked megathrust fault (Audet et al, 2009;Abers et al, 2009;Janiszewski & Abers, 2015). However, there are mulReceiver functions using OBS data 3 tiple complications related to receiver functions using OBS data and in fact very few studies have reported unambiguous results (e.g.…”

Section: Introductionmentioning

confidence: 99%

Receiver functions using OBS data: promises and limitations from numerical modelling and examples from the Cascadia Initiative

Audet¹

2016

Geophys. J. Int.

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SUMMARYThe expanding fleet of broadband ocean-bottom seismograph (OBS) stations is facilitating the study of the structure and seismicity of oceanic plates at regional scales. For continental studies, an important tool to characterize continental crust and mantle structure is the analysis of teleseismic P receiver functions. In the oceans, however, receiver functions potentially suffer from several limiting factors that are unique to ocean sites and plate structures. In this study we model receiver functions for a variety of oceanic lithospheric structures to investigate the possibilities and limitations of receiver functions using OBS data. Several potentially contaminating effects are examined, including pressure reverberations from the water column for various ocean-floor depths and the effects of a layer of low-velocity marine sediments. These modelling results indicate that receiver functions from OBS data are difficult to interpret in the presence of marine sediments, but shallow-water sites in subduction zone forearcs may be suitable for constraining various crustal elements around the locked megathrust fault. We propose using a complementary approach based on transfer function modelling combined with a grid search approach that bypasses receiver functions altogether and estimates model properties directly from minimally processed waveforms. Using real data examples from the Cascadia Initiative, we show how receiver and transfer functions can be used to infer seismic properties of the oceanic plate in both shallow (Cascadia forearc) and deep (Juan de Fuca Ridge) ocean settings.

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“…Note as well that one of the strongest signals in the RF sweeps is a negative-polarity pulse at 5.0-5.5 s delay. The expected timing for the negative-polarity ocean reverberation [Janiszewski and Abers, 2015] for the T06 station depth of 4.71 km, however, is roughly 6.3 s. At this time-delay, the ZR-RF sweep does not have a clear signal.…”

Section: Stations With Sediment Resonancementioning

confidence: 86%

“…We assert, however, that 1-D models of this resonance are too extreme, and a more detailed treatment will be necessary. Similar sediment resonance behavior in the Cascadia region has not prevented the use of seafloor receiver functions to investigate mantle and subduction-zone structure [Janiszewski and Abers, 2015], though their resolution is thus far greatly limited relative to land-based seismic observations. We stand by our inferences of direct Ps signals that plausibly relate to the seismic LAB beneath ocean floor that has not been altered by postspreading volcanism.…”

Section: 1002/2016gc006453mentioning

confidence: 99%

Reply to comment by Kawakatsu and Abe on “Nature of the seismic lithosphere‐asthenosphere boundary within normal oceanic mantle from high‐resolution receiver functions”

Olugboji

Park

Karato

2016

Geochem Geophys Geosyst

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Kawakatsu and Abe (2016) have highlighted the potential complicating effect of sediment reverberations on the analysis and interpretation of crust and mantle phases inferred from receiver functions analyzed from ocean-bottom seismograms. In their comment, they identify resonant peaks in the power spectrum at one of the stations, T06, and demonstrate with synthetic modeling how sedimentinduced resonances can cause instability in the recovered receiver-function (RF) traces. They also request a detailed explanation of how LQT rotation is conducted, and why its use leads to stable receiver functions in the analysis of . We welcome this query as an opportunity to highlight certain technical aspects of the data-analysis procedures used in . Our methods derive partly from methods recommended by previous studies of receiver functions estimated from seismic seafloor data, particularly the use of the modal wavefield decomposition (which we approximated by the LQT rotation) to suppress reverberation signals in the overlying water column. Approach Used in Calculating Receiver FunctionWe use multiple-taper correlation (MTC) to estimate receiver functions [Park and Levin, 2000], which estimates Ps converted-waves from the portions of the P, SV, and SH motions that are mutually coherent in narrow band-passes (J. Park and V. Levin, Statistics and frequency-domain moveout for multiple-taper receiver functions, submitted to Geophysical Journal International, 2016), discarding the incoherent portion of the wavefield. We apply moveout corrections to the MTC RFs before stacking in the frequency domain to enhance primary Ps conversions from deep interfaces, and suppress reverberations [Helffrich, 2006;Bianchi et al, 2010] (Park and Levin, submitted manuscript, 2016). Finally, synthetic modeling suggests that, even at our noisiest stations, defocusing of seismic energy within the sediment layer leads to reverberations of much smaller amplitude than predicted by simple 1-D models. Real seafloor seismic observations exhibit other evidence for resonant behavior that plausibly arise from ambient motions at the seafloor, because they can be detected in the seismic noise prior to P-wave arrival. Our identification of the deep LAB interface relies on the observed moveout of its negative-amplitude Ps with epicentral distance, when we analyze P-coda for receiver functions. This Ps conversion (with moveout) is absent when preevent data are analyzed. Adjustable Empirical LQT RotationWe use an empirical LQT rotation as an approximate method of wave-field decomposition [e.g., Vinnik, 1977;Bostock, 1998;Reading et al., 2003;Svenningsen, 2004]. An explicit modal wave-field decomposition is advocated by Bostock and Trehu [2012] to reduce contamination of water and sediment reverberations. The modal decomposition relies on either a collocated seafloor pressure sensor or prior knowledge of the sediment layer to effect its correction. The LQT rotation is crude by comparison, but can be scaled to less than a full rotation.We used an empirical r...

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Imaging the Plate Interface in the Cascadia Seismogenic Zone: New Constraints from Offshore Receiver Functions

Cited by 56 publications

References 42 publications

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

Receiver functions using OBS data: promises and limitations from numerical modelling and examples from the Cascadia Initiative

Reply to comment by Kawakatsu and Abe on “Nature of the seismic lithosphere‐asthenosphere boundary within normal oceanic mantle from high‐resolution receiver functions”

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