Complex Structure in the Nootka Fault Zone Revealed by Double‐Difference Tomography and a New Earthquake Catalog

Merrill, R.; Bostock, M. G.; Peacock, Simon M.; Schaeffer, A. J.; Roecker, S. W.

doi:10.1029/2021gc010205

Cited by 11 publications

(16 citation statements)

References 48 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The REST algorithm has been used successfully in other studies involving hypocenter catalog generation (e.g., Comte et al., 2017, 2019, 2023; Lanza et al., 2019; Littel et al., 2023; Merrill et al., 2022; Yarce et al., 2023) but is still a relatively untested procedure and its efficacy has not been extensively documented. In any event, its performance is likely to be somewhat dependent on the specifics of a given data set.…”

Section: Data and Processingmentioning

confidence: 99%

Are Volatiles From Subducted Ridges on the Pampean Flat Slab Fracking the Crust? Evidence From an Enhanced Seismicity Catalog

Maharaj,

Roecker,

Alvarado

et al. 2023

Geochem Geophys Geosyst

View full text Add to dashboard Cite

Seamounts and ridges are often invoked to explain subduction‐related phenomena such as flat slab generation, but the extent of their involvement remains controversial. An analysis of seismicity in the region of the Pampean flat slab through an application of an automated catalog generation algorithm resulted in 35,924 well constrained local earthquake hypocenters and a total of 12,172 focal mechanisms. Several new features related to the subduction of the Juan Fernandez Ridge (JFR) were discovered, including (a) a series of parallel lineaments of seismicity in the subducted Nazca plate separated by about 50 km and trending about 20°, and (b) a strong spatial correlation between these deeper (>80 km depth) regions of intense seismicity and concentrations of activity in the crust almost directly above it. Focal mechanisms of the deeper events are almost exclusively (∼81%) normal, while those in the crust are predominantly (∼70%) reverse. The deeper lineaments mirror the orientation and spacing of several seamount chains seen on the Nazca plate, suggesting that these patterns are caused by the same types of features at depth. This would imply that relatively minor features persist as slab anomalies long after they are subducted. The correlation of the deeper seismicity that defines these features with seismicity in the mid to lower crust suggests a genetic relation between the two. We postulate that volatiles from the subducted ridges percolate into the South American crust and induce seismicity essentially by fracking it.

show abstract

Section: Data and Processingmentioning

confidence: 99%

Are Volatiles From Subducted Ridges on the Pampean Flat Slab Fracking the Crust? Evidence From an Enhanced Seismicity Catalog

Maharaj,

Roecker,

Alvarado

et al. 2023

Geochem Geophys Geosyst

View full text Add to dashboard Cite

show abstract

“…The c horizon generally follows the LFE locations (Savard et al., 2020). Substantial scatter in the station measurements and difficulties in reconciling phase correlations across closely spaced stations attest to the complex subsurface structures that are also evident in the local seismic tomography and may be related to the subduction of the Nootka Fault Zone as the northern terminus of JdF subduction (Figure 8b, Merrill et al., 2022; Savard et al., 2018).…”

Section: Resultsmentioning

confidence: 99%

“…To the south, the Gorda micro‐plate subducts at 33 mm yr −1 with an azimuth of N52°E (DeMets et al., 1994). The Explorer plate to the north does not subduct but more likely underthrusts the North American Plate beneath northern Vancouver Island (Audet et al., 2008; Merrill et al., 2022; Riddihough, 1984; Savard et al., 2020). To the north, the subduction system transforms into the right‐lateral Queen Charlotte and Revere‐Dellwood Faults and to the south into the San Andreas Fault (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

A Cascadia Slab Model From Receiver Functions

Bloch,

Bostock,

Audet

2023

Geochem Geophys Geosyst

Self Cite

View full text Add to dashboard Cite

We map the characteristic signature of the subducting Juan de Fuca and Gorda plates along the entire Cascadia forearc from northern Vancouver Island, Canada, to Cape Mendocino in northern California, USA, using teleseismic receiver functions. The subducting oceanic crustal complex, possibly including subcreted material, is parameterized by three horizons capable of generating mode‐converted waves: a negative velocity contrast at the top of a low velocity zone underlain by two horizons representing positive contrasts. The amplitude of the conversions varies likely due to differences in composition and/or fluid content. We analyzed the slab signature for 298 long‐running land seismic stations, estimated the depth of the three interfaces through inverse modeling and fitted regularized spline surfaces through the station control points to construct a margin‐wide, double‐layered slab model. Crystalline terranes that act as the static backstop appear to form the major structural barrier that controls the slab morphology. Where the backstop recedes landward beneath the Olympic Peninsula and Cape Mendocino, the slab subducts sub‐horizontally, while the seaward‐protruding and thickened Siletz terrane beneath central Oregon causes steepening of the slab. A tight bend in slab morphology south of the Olympic Peninsula coincides with the location of recurring large intermediate depth earthquakes. The top‐to‐Moho thickness of the slab generally exceeds the thickness of the oceanic crust by 2–12 km, suggesting thickening of the slab or underplating of slab material to the overriding North American plate.

show abstract

“…As the variations in waveforms made the application of simple cross correlation untenable, and given the signals characteristics, we considered that we did not have a suitable catalog to train a Machine Learning approach, we investigated an alternate approach at onset estimation using the Regressive ESTimator (REST) (e.g., Comte et al, 2019;Lanza et al, 2019;Merrill et al, 2022) package that is normally used to generate catalogs of earthquake recorded by local seismic networks. Our motivation for this choice is that REST does not require any a priori knowledge of waveform morphology (i.e., it does not have to be "trained"), and hence can cope with highly variable waveforms.…”

Section: Application Of the Regressive Estimator (Rest)mentioning

confidence: 99%

CORREL: Automated Onset Estimation for Controlled-Source Seismic Experiments

Reyes-Wagner

Comte

Roecker

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

Estimates of the onset times of P phases from active source experiments can effectively be used in developing wavespeed models, and the large number of recordings typical of such experiments incentivizes the development of automated approaches to generate these estimates. The simplicity and repeatability of an airgun source such as that used in the 2016 Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source (PICTURES) project in northern Chile suggested that a straightforward application of waveform cross-correlation would suffice for arrivals recorded by a network of inland seismic stations, but did not work well due to significant variations in waveform morphology. Application of an alternative algorithm typically used in passive source investigations, the Regressive ESTimator (REST) autopicking package, also proved unsatisfactory, largely because the limited spectral bandwidth of the airgun source and the frequent occurrence of local seismicity led to numerous false picks. This motivated the development of a new approach, named CORREL, that is a hybrid of REST and cross-correlation, with the addition of a constraint in the form of a polynomial function based on the REST picks that provides a reasonable prediction of an onset time. Compared to the results obtained originally from REST and simple waveform correlation, the application of CORREL to the PICTURES data both significantly increased the number of arrivals detected and greatly reduced the number of outliers. The predictive polynomial also provides CORREL a better means to discriminate true shots from the abundant natural seismicity.

show abstract

Complex Structure in the Nootka Fault Zone Revealed by Double‐Difference Tomography and a New Earthquake Catalog

Cited by 11 publications

References 48 publications

Are Volatiles From Subducted Ridges on the Pampean Flat Slab Fracking the Crust? Evidence From an Enhanced Seismicity Catalog

Are Volatiles From Subducted Ridges on the Pampean Flat Slab Fracking the Crust? Evidence From an Enhanced Seismicity Catalog

A Cascadia Slab Model From Receiver Functions

CORREL: Automated Onset Estimation for Controlled-Source Seismic Experiments

Contact Info

Product

Resources

About