TY - JOUR T1 - Temporal Relationship of Slow Slip Events and Microearthquake Seismicity: Insights From Earthquake Automatic Detections in the Northern Hikurangi Margin, Aotearoa New Zealand JF - Geochemistry, Geophysics, Geosystems Y1 - 2023 A1 - Yarce, Jefferson A1 - Sheehan, Anne F. A1 - Roecker, Steven KW - earthquake detection KW - Hikurangi KW - ocean bottom seismometers KW - seismicity KW - slow slip event KW - subduction AB - Slow slip events in the northern Hikurangi margin of Aotearoa New Zealand occur every 18–24 months and last for several weeks before returning to average convergence rates of around 38 mm/yr. Along this plate boundary, the Hikurangi plateau subducts beneath the overlying Australian plate and slow slip events occur along their plate interface at depths between 2 and 15 km. To explore whether there is a temporal relationship between slow slip events and earthquake occurrence, the Regressive ESTimator automated phase arrival detection and onset estimation algorithm was applied to a data set of continuous waveform data collected by both land and ocean bottom seismometers. This detector uses an autoregressive algorithm with iterative refinement to first detect seismic events and then create a catalog of hypocenters and P and S wave arrival times. Results are compared with an available catalog of manually detected seismic events. The auto-detector was able to find more than three times the number of events detected by analysts. With our newly assembled data set of automatically detected earthquakes, we were able to determine that there was an increase in the rate of earthquake occurrence during the 2014 slow slip event. VL - 24 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2022GC010537 IS - 3 N1 - _eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2022GC010537 ER - TY - JOUR T1 - Continuous Tremor Activity With Stable Polarization Direction Following the 2014 Large Slow Slip Event in the Hikurangi Subduction Margin Offshore New Zealand JF - Journal of Geophysical Research: Solid Earth Y1 - 2022 A1 - Iwasaki, Yuriko A1 - Mochizuki, Kimihiro A1 - Ishise, Motoko A1 - Todd, Erin K. A1 - Schwartz, Susan Y. A1 - Zal, Hubert A1 - Savage, Martha K. A1 - Henrys, Stuart A1 - Sheehan, Anne F. A1 - Ito, Yoshihiro A1 - Wallace, Laura M. A1 - Webb, Spahr C. A1 - Yamada, Tomoaki A1 - Shinohara, Masanao KW - New Zealand KW - polarization KW - S-wave splitting KW - Seamount KW - slow slip KW - tremor AB - Many types of slow earthquakes have been discovered at subduction zones around the world. However, the physical process of these slow earthquakes is not well understood. To monitor offshore slow earthquakes, a marine seismic and geodetic experiment was conducted at the Hikurangi subduction margin from May 2014 to June 2015. During this experiment, a large slow slip event (Mw 6.8) occurred directly beneath the ocean bottom seismometer (OBS) network. In this study, S-wave splitting and polarization analysis methods, which have been previously used on onshore data to investigate tremor and anisotropy, are applied to continuous OBS waveform data to identify tremors that are too small to detect by the envelope cross correlation method. Continuous tremor activity with stable polarization directions is detected at the end of the 2014 slow slip event and continued for about 2 weeks. The tremors are generated around a southwest bend in the slow slip contours and at the landward edge of a subducted seamount. Our findings corroborate a previous interpretation, based on burst-type repeating earthquakes and intermittent tremor, that localized slow slip and tremor around the seamount was triggered by fluid migration following the large plate boundary slow slip event and indicate tremor occurred continuously rather than as isolated and sporadic individual events. VL - 127 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2021JB022161 N1 - _eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021JB022161 ER - TY - JOUR T1 - Near Trench 3D Seismic Attenuation Offshore Northern Hikurangi Subduction Margin, North Island, New Zealand JF - Journal of Geophysical Research: Solid Earth Y1 - 2021 A1 - Nakai, Jenny S. A1 - Sheehan, Anne F. A1 - Abercrombie, Rachel E. A1 - Eberhart-Phillips, Donna KW - fluids KW - seismic attenuation KW - subduction zone AB - We image seismic attenuation near the Hikurangi trench offshore New Zealand, using ocean bottom and land-based seismometers, revealing high attenuation above a recurring shallow slow-slip event and within the subducting Hikurangi Plateau. The Hikurangi subduction margin east of the North Island, New Zealand is the site of frequent shallow slow slip events. Overpressured fluids are hypothesized to lead to slow slip at shallow depths close to the oceanic trench. Seismic attenuation, energy loss of seismic waves, can be used to detect high temperatures, melt, the presence of fluids, and fractures. We use local earthquake P- and S-waves from 180 earthquakes to invert for t*, and subsequently invert for Qp and Qs, offshore the North Island directly above the area of slow slip. We image Qp and Qs to ∼25 km depth, increasing resolution of previously identified coastal low Q (100–300), and finding a new region of even higher attenuation (Qp and Qs < 50–100) directly above the shallow slow slip event of 2014–2015, beneath the offshore seismic array. This highest attenuation is downdip of a subducting seamount, and is spatially correlated with a high seismic reflectivity zone and Vp/Vs > 1.85, all of which provide evidence for the presence of fluids. The Qp and Qs is low at the trench (<50–100) and in the subducting plate (100–200), suggesting that seismic wave scattering due to faults, fractures, and the inherent heterogeneous composition of the Hikurangi Plateau, a large igneous province, plays a role in seismic attenuation. VL - 126 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2020JB020810 N1 - _eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020JB020810 ER - TY - JOUR T1 - The Alaska Amphibious Community Seismic Experiment JF - Seismological Research Letters Y1 - 2020 A1 - Barcheck, Grace A1 - Abers, Geoffrey A. A1 - Adams, Aubreya N. A1 - Bécel, Anne A1 - Collins, John A1 - Gaherty, James B. A1 - Haeussler, Peter J. A1 - Li, Zongshan A1 - Moore, Ginevra A1 - Onyango, Evans A1 - Roland, Emily A1 - Sampson, Daniel E. A1 - Schwartz, Susan Y. A1 - Sheehan, Anne F. A1 - Shillington, Donna J. A1 - Shore, Patrick J. A1 - Webb, Spahr A1 - Wiens, Douglas A. A1 - Worthington, Lindsay L. AB - The Alaska Amphibious Community Seismic Experiment (AACSE) is a shoreline‐crossing passive‐ and active‐source seismic experiment that took place from May 2018 through August 2019 along an ∼700  km long section of the Aleutian subduction zone spanning Kodiak Island and the Alaska Peninsula. The experiment featured 105 broadband seismometers; 30 were deployed onshore, and 75 were deployed offshore in Ocean Bottom Seismometer (OBS) packages. Additional strong‐motion instruments were also deployed at six onshore seismic sites. Offshore OBS stretched from the outer rise across the trench to the shelf. OBSs in shallow water (<262  m depth) were deployed with a trawl‐resistant shield, and deeper OBSs were unshielded. Additionally, a number of OBS‐mounted strong‐motion instruments, differential and absolute pressure gauges, hydrophones, and temperature and salinity sensors were deployed. OBSs were deployed on two cruises of the R/V Sikuliaq in May and July 2018 and retrieved on two cruises aboard the R/V Sikuliaq and R/V Langseth in August–September 2019. A complementary 398‐instrument nodal seismometer array was deployed on Kodiak Island for four weeks in May–June 2019, and an active‐source seismic survey on the R/V Langseth was arranged in June 2019 to shoot into the AACSE broadband network and the nodes. Additional underway data from cruises include seafloor bathymetry and sub‐bottom profiles, with extra data collected near the rupture zone of the 2018 Mw 7.9 offshore‐Kodiak earthquake. The AACSE network was deployed simultaneously with the EarthScope Transportable Array (TA) in Alaska, effectively densifying and extending the TA offshore in the region of the Alaska Peninsula. AACSE is a community experiment, and all data were made available publicly as soon as feasible in appropriate repositories. VL - 91 UR - https://doi.org/10.1785/0220200189 ER - TY - JOUR T1 - Improving Forecast Accuracy With Tsunami Data Assimilation: The 2009 Dusky Sound, New Zealand, Tsunami JF - Journal of Geophysical Research: Solid Earth Y1 - 2019 A1 - Sheehan, Anne F. A1 - Gusman, Aditya R. A1 - Satake, Kenji VL - 124 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2018JB016575 ER - TY - JOUR T1 - Earthquakes and Tremor Linked to Seamount Subduction During Shallow Slow Slip at the Hikurangi Margin, New Zealand JF - Journal of Geophysical Research: Solid Earth Y1 - 2018 A1 - Todd, Erin K. A1 - Schwartz, Susan Y. A1 - Mochizuki, Kimihiro A1 - Wallace, Laura M. A1 - Sheehan, Anne F. A1 - Webb, Spahr C. A1 - Williams, Charles A. A1 - Nakai, Jenny A1 - Yarce, Jefferson A1 - Fry, Bill A1 - Henrys, Stuart A1 - Ito, Yoshihiro KW - earthquake KW - New Zealand KW - Seamount KW - slow slip KW - subduction KW - tremor AB - Shallow slow slip events have been well documented offshore Gisborne at the northern Hikurangi subduction margin, New Zealand, and are associated with tectonic tremor downdip of the slow slip patch and increases in local microseismicity. Tremor and seismicity on the shallow subduction interface are often poorly resolved due to their distance from land-based seismic and geodetic networks. To address this shortcoming, the Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip experiment deployed 24 absolute pressure gauges and 15 ocean bottom seismometers on the seafloor above the Gisborne slow slip patch to investigate the spatial and temporal extent of slow slip and associated tremor and earthquake activity. We present a detailed spatiotemporal analysis of the seismic signatures of various interplate slip processes associated with the September/October 2014 Gisborne slow slip event. Tectonic tremor begins toward the end and continues after the geodetically constrained slow slip event and is localized in the vicinity of two subducted seamounts within and updip of the slow slip patch. The subsequent, rather than synchronous occurrence of tremor suggests that tremor may be triggered by stress changes induced by slow slip. However, Coulomb failure stress change models based on the slow slip distribution fail to predict the location of tremor, suggesting that seamount subduction plays a dominant role in the stress state of the shallow megathrust. This and the observed interplay of seismic and aseismic interplate slip processes imply that stress changes from slow slip play a secondary role in the distribution of associated microseismicity. VL - 123 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2018JB016136 N1 - _eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018JB016136 ER - TY - JOUR T1 - Teleseismic S-wave tomography of South Island, New Zealand upper mantle JF - Geosphere Y1 - 2018 A1 - Zietlow, Daniel W. A1 - Sheehan, Anne F. A1 - Bernardino, Melissa V. VL - 14 UR - https://pubs.geoscienceworld.org/gsa/geosphere/article/14/3/1343/530581/Teleseismic-Swave-tomography-of-South-Island-New ER - TY - JOUR T1 - Offshore Rayleigh group velocity observations of the South Island, New Zealand, from ambient noise data JF - Geophysical Journal International Y1 - 2017 A1 - Yeck, William L. A1 - Sheehan, Anne F. A1 - Stachnik, Joshua C. A1 - Lin, Fan-Chi VL - 209 UR - https://academic.oup.com/gji/article/209/2/827/2998716 ER - TY - JOUR T1 - Remote detection of cryoacoustic signals using noise interferometry of seafloor pressure data JF - The Journal of the Acoustical Society of America Y1 - 2017 A1 - Ball, Justin S. A1 - Sheehan, Anne F. A1 - Scambos, Ted VL - 141 UR - https://asa.scitation.org/doi/10.1121/1.4989358 N1 - Publisher: Acoustical Society of America ER - TY - JOUR T1 - Lithospheric shear velocity structure of South Island, New Zealand, from amphibious Rayleigh wave tomography JF - Journal of Geophysical Research: Solid Earth Y1 - 2016 A1 - Ball, Justin S. A1 - Sheehan, Anne F. A1 - Stachnik, Joshua C. A1 - Lin, Fan-Chi A1 - Yeck, William L. A1 - Collins, John A. VL - 121 UR - http://doi.wiley.com/10.1002/2015JB012726 ER - TY - JOUR T1 - Teleseismic P wave tomography of South Island, New Zealand upper mantle: Evidence of subduction of Pacific lithosphere since 45 Ma JF - Journal of Geophysical Research: Solid Earth Y1 - 2016 A1 - Zietlow, Daniel W. A1 - Molnar, Peter H. A1 - Sheehan, Anne F. VL - 121 UR - http://doi.wiley.com/10.1002/2015JB012624 ER - TY - JOUR T1 - Tsunami data assimilation of Cascadia seafloor pressure gauge records from the 2012 Haida Gwaii earthquake JF - Geophysical Research Letters Y1 - 2016 A1 - Gusman, Aditya Riadi A1 - Sheehan, Anne F. A1 - Satake, Kenji A1 - Heidarzadeh, Mohammad A1 - Mulia, Iyan Eka A1 - Maeda, Takuto VL - 43 UR - http://doi.wiley.com/10.1002/2016GL068368 ER - TY - JOUR T1 - Array Observations of the 2012 Haida Gwaii Tsunami Using Cascadia Initiative Absolute and Differential Seafloor Pressure Gauges JF - Seismological Research Letters Y1 - 2015 A1 - Sheehan, Anne F. A1 - Gusman, Aditya Riadi A1 - Heidarzadeh, Mohammad A1 - Satake, Kenji VL - 86 UR - https://pubs.geoscienceworld.org/srl/article/86/5/1278-1286/315554 ER - TY - JOUR T1 - Interferometry of infragravity waves off New Zealand JF - Journal of Geophysical Research: Oceans Y1 - 2014 A1 - Godin, Oleg A. A1 - Zabotin, Nikolay A. A1 - Sheehan, Anne F. A1 - Collins, John A. KW - deep ocean KW - random wave fields KW - Surface gravity waves KW - wave interferometry AB - AbstractWave interferometry is a remote sensing technique, which is increasingly employed in helioseismology, seismology, and acoustics to retrieve parameters of the propagation medium from two-point cross-correlation functions of random wavefields. Here we apply interferometry to yearlong records of seafloor pressure at 28 locations off New Zealand's South Island to investigate propagation and directivity properties of infragravity waves away from shore. A compressed cross-correlation function technique is proposed to make the interferometry of dispersive waves more robust, decrease the necessary noise averaging time, and simplify retrieval of quantitative information from noise cross correlations. The emergence of deterministic wave arrivals from cross correlations of random wavefields is observed up to the maximum range of 692 km between the pressure sensors in the array. Free, linear waves with a strongly anisotropic distribution of power flux density are found to be dominant in the infragravity wavefield. Lowest-frequency components of the infragravity wavefield are largely isotropic. The anisotropy has its maximum in the middle of the spectral band and decreases at the high-frequency end of the spectrum. Highest anisotropy peaks correspond to waves coming from portions of the New Zealand's shoreline. Significant contributions are also observed from waves propagating along the coastline and probably coming from powerful sources in the northeast Pacific. Infragravity wave directivity is markedly different to the east and to the west of the South Island. The northwest coast of the South Island is found to be a net source of the infragravity wave energy. VL - 119 UR - https://onlinelibrary.wiley.com/doi/abs/10.1002/2013JC009395 N1 - _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/2013JC009395 ER - TY - JOUR T1 - A joint Monte Carlo analysis of seafloor compliance, Rayleigh wave dispersion and receiver functions at ocean bottom seismic stations offshore New Zealand JF - Geochemistry, Geophysics, Geosystems Y1 - 2014 A1 - Ball, Justin S. A1 - Sheehan, Anne F. A1 - Stachnik, Joshua C. A1 - Lin, Fan-Chi A1 - Collins, John A. KW - Monte Carlo KW - New Zealand KW - OBS receiver function KW - seafloor compliance KW - sediment shear modes KW - surface waves AB - Teleseismic body-wave imaging techniques such as receiver function analysis can be notoriously difficult to employ on ocean-bottom seismic data due largely to multiple reverberations within the water and low-velocity sediments. In lieu of suppressing this coherently scattered noise in ocean-bottom receiver functions, these site effects can be modeled in conjunction with shear velocity information from seafloor compliance and surface wave dispersion measurements to discern crustal structure. A novel technique to estimate 1-D crustal shear-velocity profiles from these data using Monte Carlo sampling is presented here. We find that seafloor compliance inversions and P-S conversions observed in the receiver functions provide complimentary constraints on sediment velocity and thickness. Incoherent noise in receiver functions from the MOANA ocean bottom seismic experiment limit the accuracy of the practical analysis at crustal scales, but synthetic recovery tests and comparison with independent unconstrained nonlinear optimization results affirm the utility of this technique in principle. VL - 15 UR - https://onlinelibrary.wiley.com/doi/abs/10.1002/2014GC005412 N1 - _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/2014GC005412 ER - TY - JOUR T1 - Upper mantle seismic anisotropy at a strike-slip boundary: South Island, New Zealand JF - Journal of Geophysical Research: Solid Earth Y1 - 2014 A1 - Zietlow, Daniel W. A1 - Sheehan, Anne F. A1 - Molnar, Peter H. A1 - Savage, Martha K. A1 - Hirth, Greg A1 - Collins, John A. A1 - Hager, Bradford H. KW - mantle lithosphere KW - MOANA KW - New Zealand KW - ocean bottom seismometers KW - seismic anisotropy KW - South Island AB - New shear wave splitting measurements made from stations onshore and offshore the South Island of New Zealand show a zone of anisotropy 100–200 km wide. Measurements in central South Island and up to approximately 100 km offshore from the west coast yield orientations of the fast quasi-shear wave nearly parallel to relative plate motion, with increased obliquity to this orientation observed farther from shore. On the eastern side of the island, fast orientations rotate counterclockwise to become nearly perpendicular to the orientation of relative plate motion approximately 200 km off the east coast. Uniform delay times between the fast and slow quasi-shear waves of nearly 2.0 s onshore continue to stations approximately 100 km off the west coast, after which they decrease to 1 s at 200 km. Stations more than 300 km from the west coast show little to no splitting. East coast stations have delay times around 1 s. Simple strain fields calculated from a thin viscous sheet model (representing distributed lithospheric deformation) with strain rates decreasing exponentially to both the northwest and southeast with e-folding dimensions of 25–35 km (approximately 75% of the deformation within a zone 100–140 km wide) match orientations and amounts of observed splitting. A model of deformation localized in the lithosphere and then spreading out in the asthenosphere also yields predictions consistent with observed splitting if, at depths of 100–130 km below the lithosphere, typical grain sizes are 6–7 mm. VL - 119 UR - https://onlinelibrary.wiley.com/doi/abs/10.1002/2013JB010676 N1 - _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/2013JB010676 ER - TY - JOUR T1 - Power spectra of infragravity waves in a deep ocean JF - Geophysical Research Letters Y1 - 2013 A1 - Godin, Oleg A. A1 - Zabotin, Nikolay A. A1 - Sheehan, Anne F. A1 - Yang, Zhaohui A1 - Collins, John A. KW - deep ocean KW - random wave fields KW - Surface gravity waves KW - wave spectra AB - AbstractInfragravity waves (IGWs) play an important role in coupling wave processes in the ocean, ice shelves, atmosphere, and the solid Earth. Due to the paucity of experimental data, little quantitative information is available about power spectra of IGWs away from the shore. Here we use continuous, yearlong records of pressure at 28 locations on the seafloor off New Zealand's South Island to investigate spectral and spatial distribution of IGW energy. Dimensional analysis of diffuse IGW fields reveals universal properties of the power spectra observed at different water depths and leads to a simple, predictive model of the IGW spectra. While sources of IGWs off New Zealand are found to have a flat power spectrum, the IGW energy density has a pronounced dependence on frequency and local water depth as a result of the interaction of the waves with varying bathymetry. VL - 40 UR - https://onlinelibrary.wiley.com/doi/abs/10.1002/grl.50418 N1 - _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/grl.50418 ER - TY - JOUR T1 - The character of seafloor ambient noise recorded offshore New Zealand: Results from the MOANA ocean bottom seismic experiment JF - Geochemistry, Geophysics, Geosystems Y1 - 2012 A1 - Yang, Zhaohui A1 - Sheehan, Anne F. A1 - Collins, John A. A1 - Laske, Gabi KW - continental shelf KW - infragravity wave KW - New Zealand KW - noise KW - OBS AB - {We analyze the characteristics of ambient noise recorded on ocean-bottom seismographs using data from the 2009–2010 MOANA (Marine Observations of Anisotropy Near Aotearoa) seismic experiment deployed west and east of South Island, New Zealand. Microseism and infragravity noise peaks are clear on data recorded on the vertical channel of the seismometer and on the pressure sensor. The noise levels in the infragravity band (<0.03 Hz) on the horizontal seismometer channels are too high to show the infragravity peak. There is a small difference (∼0.25 Hz versus ∼0.2 Hz) in microseism peak frequencies between the two sides of the South Island on all three seismic channels. Our results show clear depth dependence between the peak frequency of infragravity waves and the water depth. We find that the product of water depth and wave number at the peak frequency is a constant VL - 13 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2012GC004201 N1 - _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2012GC004201 ER -