Journal of Geophysical Research: Solid Earth最新文献

{"title":"Effects of Chemical Alteration on Frictional Properties in a Deep, Granitic, Geothermal System in Cornwall: Direct Shear Experiments at Near In Situ Conditions","authors":"N. Harpers,&nbsp;N. Forbes Inskip,&nbsp;M. J. Allen,&nbsp;J. Buckman,&nbsp;D. R. Faulkner,&nbsp;H. Claes,&nbsp;R. Shail,&nbsp;S. den Hartog,&nbsp;A. Busch","doi":"10.1029/2024JB028861","DOIUrl":"10.1029/2024JB028861","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <p>The geochemical alteration of host rocks might affect the productivity and the potential for induced seismicity of geothermal systems. In addition to natural alteration, following production and heat extraction, re-injected fluids at lower temperatures and different pressures may be in chemical disequilibrium with the rock, impacting mineral solubility and dissolution/precipitation processes. In this study, we investigate the effect of geochemical alteration on the frictional behavior of granites, and their seismogenic potential, by conducting direct shear experiments using samples with varying degrees of alteration. The samples originate from the Carnmenellis granite in Cornwall, SW England, and represent the formation used in the United Downs Deep Geothermal Power Project for heat extraction. Experiments were conducted on granite powders (referred to as gouges) at room temperature and 180°C, at simulated in situ confining and pore pressures of 130 and 50 MPa, respectively (∼5 km depth). With increasing degree of alteration, the frictional strength of the gouges decreases while frictional stability increases. At high temperature, frictional stability is reduced for all samples while maintaining the trend with alteration stage. Microstructural investigation of the sheared gouges shows alteration delocalizes shear by reducing grain size and increasing clay fraction, which promotes the formation of pervasive shear fabrics. Our work suggests that, within the range of tested pressures, more alteration of granite initially causes more stable shearing in a fault. This behavior with alteration is sustained at high temperatures, but the overall frictional stability is reduced which increases the potential for induced seismicity at higher temperatures.</p>\u0000 </section>\u0000 </div>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB028861","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142519476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Back-Propagating Rupture: Nature, Excitation, and Implications","authors":"Xiaotian Ding,&nbsp;Shiqing Xu,&nbsp;Eiichi Fukuyama,&nbsp;Futoshi Yamashita","doi":"10.1029/2024JB029629","DOIUrl":"10.1029/2024JB029629","url":null,"abstract":"<p>Recent observations show that certain rupture phase can propagate backward relative to the earlier one during a single earthquake event. Such back-propagating rupture (BPR) was not well considered by the conventional earthquake source studies and remains a mystery to the seismological community. Here we present a comprehensive analysis of BPR, by combining theoretical considerations, numerical simulations, and observational evidences. First, we argue that BPR in terms of back-propagating stress wave is an intrinsic feature during dynamic ruptures; however, its signature can be easily masked by the destructive interference behind the primary rupture front. Then, we propose an idea that perturbation to an otherwise smooth rupture process may make some phases of BPR observable. We test and verify this idea by numerically simulating rupture propagation under a variety of perturbations, including a sudden change of stress, bulk or interfacial property and fault geometry along rupture propagation path. We further cross-validate the numerical results by available observations from laboratory and natural earthquakes, and confirm that rupture “reflection” at free surface, rupture coalescence and breakage of prominent asperity are very efficient for exciting observable BPR. Based on the simulated and observed results, we classify BPR into two general types: interface wave and high-order re-rupture, depending on the stress recovery and drop before and after the arrival of BPR, respectively. Our work clarifies the nature and excitation of BPR, and can help improve the understanding of earthquake physics, the inference of fault property distribution and evolution, and the assessment of earthquake hazard.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB029629","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142490683","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pressure Monitoring of Disposal Reservoirs in North-Central Oklahoma: Implications for Seismicity and Geostorage","authors":"B. Allen,&nbsp;K. Murray,&nbsp;P. Ogwari,&nbsp;F. Suriamin,&nbsp;J. I. Walter,&nbsp;N. W. Hayman","doi":"10.1029/2024JB029200","DOIUrl":"10.1029/2024JB029200","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <p>Disposal of industrial wastewater and activities such as <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mrow>\u0000 <mi>C</mi>\u0000 <mi>O</mi>\u0000 </mrow>\u0000 <mn>2</mn>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${mathrm{C}mathrm{O}}_{2}$</annotation>\u0000 </semantics></math> underground sequestration depend upon pressure conditions within deep geologic reservoirs. Sometimes, injection and storage are associated with induced seismicity, suggested to result from reservoir compartmentalization, leakage into faults, or other mechanisms in the subsurface. To understand subsurface pressure conditions within a major regional disposal reservoir, the Arbuckle Group of Oklahoma, we monitored the water levels in 15 inactive injection wells. The wells were monitored at 30-s intervals, with eight wells monitored since September 2016, and an additional seven from July 2017. All the wells were monitored until early March 2020. Since 2016, hydraulic head decreased in 13 of the 15 wells, proportional to near-borehole fluid pressure even considering decreasing regional injection volumes during this period. The well pressures respond to three types of perturbations: (i) gravitational fluctuations (a.k.a. solid-earth tides) (ii) distal and proximal earthquakes, and (iii) injections into nearby wells. Parameterization of tidal responses illustrates that the near wellbore environments have negative fluid flux (i.e., are leaking). Earthquakes cause differing pressure responses from well to well, with some highly sensitive to proximal events, some to distal events, and some apparently insensitive. Injections have variable impacts in some cases masking tidal and earthquake pressure signals. Collectively, there appears to be a threshold injection rate above which well pressure becomes less sensitive to the volume of injections within 15 km. Multi-scale geological structure and temporal permeability changes are likely controlling the pressure field, indicating leakage of fluids across the system.</p>\u0000 </section>\u0000 </div>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB029200","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142490715","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Widespread \u0000 \u0000 \u0000 \u0000 D\u0000 \u0000 ″\u0000 \u0000 \u0000 \u0000 ${mathbf{D}}^{mathbf{{primeprime}}}$\u0000 Anisotropy Beneath North America and the Northeastern Pacific and Implications for Upper Mantle Anisotropy Measurements","authors":"Jonathan Wolf,&nbsp;Daniel A. Frost,&nbsp;Alexia Brewster,&nbsp;Maureen D. Long,&nbsp;Ed Garnero,&nbsp;John D. West","doi":"10.1029/2024JB029516","DOIUrl":"10.1029/2024JB029516","url":null,"abstract":"<p>Observations of seismic waves that have passed through the Earth's lowermost mantle provide insight into deep mantle structure and dynamics, often on relatively small spatial scales. Here we use SKS, S2KS, S3KS, and PKS signals recorded across a large region including the United States, Mexico, and Central America to study the deepest mantle beneath large swaths of North America and the northeastern Pacific Ocean. These phases are enhanced via beamforming and then used to investigate polarization- and propagation direction-dependent shear wave speeds (seismic anisotropy). A differential splitting approach enables us to robustly identify contributions from <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msup>\u0000 <mi>D</mi>\u0000 <mrow>\u0000 <mo>″</mo>\u0000 </mrow>\u0000 </msup>\u0000 </mrow>\u0000 <annotation> ${mathrm{D}}^{{primeprime}}$</annotation>\u0000 </semantics></math> anisotropy. Our results show strong seismic anisotropy in approximately half of our study region, indicating that <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msup>\u0000 <mi>D</mi>\u0000 <mrow>\u0000 <mo>″</mo>\u0000 </mrow>\u0000 </msup>\u0000 </mrow>\u0000 <annotation> ${mathrm{D}}^{{primeprime}}$</annotation>\u0000 </semantics></math> anisotropy may be more prevalent than commonly thought. In some regions, the anisotropy may be induced by flow driven by sinking cold slabs, and in other, more compact regions, by upwelling flow. Measured splitting due to lowermost mantle anisotropy is sufficiently strong to be non-negligible in interpretations of SKS splitting due to upper mantle anisotropy in certain regions, which may prompt future re-evaluations of upper mantle anisotropy beneath North and Central America.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB029516","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142490958","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Afterslip and Creep in the Rate-Dependent Framework: Joint Inversion of Borehole Strain and GNSS Displacements for the Mw 7.1 Ridgecrest Earthquake","authors":"C. Hanagan,&nbsp;R. A. Bennett,&nbsp;A. Barbour,&nbsp;A. N. Hughes","doi":"10.1029/2024JB028908","DOIUrl":"10.1029/2024JB028908","url":null,"abstract":"<p>The elusive transition toward afterslip following an earthquake is challenging to capture with typical data resolution limits. A dense geodetic network recorded the Mw 7.1 Ridgecrest earthquake, including 16 Global Navigation Satellite System (GNSS) stations and 3 borehole strainmeters (BSM). The sub-nanostrain precision and sub-second sampling rate of BSMs bridges a gap between conventional seismologic and geodetic methods, exemplified by atypical postseismic shear strain reversals observed at nearfield (&lt;2 km) station B921 that remain unexplained. We jointly invert GNSS displacements and BSM strains for coseismic and postseismic slip spanning hours to months over 7 independent periods. Cosiesmically, our model resolves the largest slip magnitudes of up to 6.6 m on the mainshock rupture plane, with similar patterns to other inferred slip distributions. The foreshock fault appears to slip coincidently with mainshock, revealing potential asperities activated during the preceding Mw 6.4 event. Postseismically, the best-fitting models adhere to mechanical rate-and-state expectations of logarithmically decaying slip adjacent to the coseismic rupture terminus, and where deep rheologic conditions favor creep. Most spatial variation occurs in the early postseismic timeframe (&lt;1–2 weeks), with evidence for regional rheologic control and static stress dependence. Triggered creep on the neighboring Garlock Fault unexpectedly persists for &gt;178 days—further highlighting the importance of fault networks in postseismic stress redistribution, critical to assessing future hazard.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142490679","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Differential Phase Analysis for Volcanic Tremor Detection and Source Location","authors":"Andrés Barajas,&nbsp;Nikolai M. Shapiro,&nbsp;German Prieto","doi":"10.1029/2024JB029010","DOIUrl":"https://doi.org/10.1029/2024JB029010","url":null,"abstract":"<p>We present observations showing that during episodes of volcanic tremors, the phase of inter-station cross-correlations becomes stable. We propose a new quantity, the phase coherence, to identify the differential phase stability in recordings obtained from a single pair of stations, which is extrapolated to the seismic network. Then, we present a new approach based on the estimation of differential travel times through the differential phase measurements, to locate the sources of tremors occurring at the end of 2015 at the Klyuchevskoy Volcanic Group in Kamchatka, Russia. We present evidence supporting the existence of two types of activity happening simultaneously during the tremor episode: the main tremor source, originating from a region located between 7 and 9 km depth under the main volcanoes, and the widespread occurrence of weak low-frequency earthquakes occurring at random locations. We show how the phase coherence and the differential phases can be used to provide information on the stability of the tremor source position and to estimate its location.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB029010","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142525526","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Particle Concentrations and Sizes for the Onset of Settling-Driven Gravitational Instabilities: Experimental Validation and Application to Volcanic Ash Clouds","authors":"Allan Fries,&nbsp;Jonathan Lemus,&nbsp;Paul A. Jarvis,&nbsp;Amanda B. Clarke,&nbsp;Jeremy C. Phillips,&nbsp;Irene Manzella,&nbsp;Costanza Bonadonna","doi":"10.1029/2024JB029117","DOIUrl":"10.1029/2024JB029117","url":null,"abstract":"<p>Settling-driven gravitational instabilities (SDGIs) can form at the base of buoyant particle-laden suspensions, modulating particle sedimentation in various settings such as meteorological and volcanic clouds, fluvial plumes, magma chambers, submarine hydrothermal plumes, or industrial emissions. These instabilities result in the formation of rapidly descending currents called ‘fingers’ within which fine particles settle faster collectively than individually. This study investigates SDGI triggering conditions underneath volcanic ash clouds through analogue experiments considering sedimentation from aqueous particle suspensions. We confirm that the conditions for which SDGIs develop are controlled by two dimensionless numbers: <i>B</i>_<i>f</i> (ratio of the characteristic finger velocity to the individual particle settling velocity); and <i>B</i>_<i>i</i> (ratio of timescale for individual particle settling to that for collective settling controlled by inertial drag). SDGIs are triggered for values of <i>B</i>_<i>f</i> and <i>B</i>_<i>i</i> &gt; 1 for which particles are fully coupled with the flow within fingers. Using these parameters, we produce a regime diagram for the 2010 eruption of Eyjafjallajökull (Iceland) that describes particle settling as a function of particle concentration and size. More studies are needed to produce a general regime diagram accounting for the evolution of SDGIs properties with eruption and atmospheric parameters. Nonetheless, our study confirms that fingers affect sedimentation from volcanic clouds with high ash volume fractions above 10⁻⁶ vol.%. Our validation of criteria predicting the onset of fingers due to SDGIs constitutes a step forward toward the incorporation of these collective settling processes in volcanic ash transport and dispersion models.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024JB029117","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142490693","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Decoding Stress Patterns of the 2023 Türkiye-Syria Earthquake Doublet","authors":"Jianquan Chen,&nbsp;Chang Liu,&nbsp;Luca Dal Zilio,&nbsp;Jianling Cao,&nbsp;Hui Wang,&nbsp;Guangliang Yang,&nbsp;Oğuz H. Göğüş,&nbsp;Hang Zhang,&nbsp;Yaolin Shi","doi":"10.1029/2024JB029213","DOIUrl":"10.1029/2024JB029213","url":null,"abstract":"<p>Earthquake interaction across multiple time scales can reveal complex stress evolution and rupture patterns. Here, we investigate the role of static stress change in the 2023 Mw 7.8 and 7.6 earthquake doublet along the East Anatolian Fault (EAF), using simulations of 19 historical earthquakes (M ≥ 6.1) and the 2023 earthquake doublet from 1822 to 2023. Focusing on six cascading sub-events during the 2023 Kahramanmaraş earthquake doublet, we reveal how one sub-event's stress alteration can impact the emergence and rupture of subsequent sub-events. Our analysis unveils that the 2023 Mw 7.8 earthquake was delayed due to stress shadow effects from historical events, while the 2023 Mw 7.6 earthquake was accelerated as a result of stress increases from historical events and ultimately triggered by the 2023 Mw 7.8 earthquake. This study underscores the importance of grasping earthquake preparation, rupture initiation, propagation, and termination in the context of intricate fault systems worldwide. Based on these results, we draw attention to increased seismic hazards in the Elazig-Bingol seismic gap of the EAF and the northern section of the Dead Sea Fault (DSF), necessitating increased monitoring and preparedness efforts.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142490957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Locating Boundaries Between Locked and Creeping Regions at Nankai and Cascadia Subduction Zones","authors":"E. M. Sherrill,&nbsp;K. M. Johnson,&nbsp;N. M. Jackson","doi":"10.1029/2024JB029346","DOIUrl":"10.1029/2024JB029346","url":null,"abstract":"<p>Interseismic coupling maps and, especially, estimates of the location of the fully coupled (locked) zone relative to the trench, coastline, and slow slip events are crucial for determining megathrust earthquake hazard at subduction zones. We present an interseismic coupling inversion that estimates the locations of the upper and lower boundaries of the locked zone, the lower boundary of the deep transition zone, and downdip gradient of creep rate in the transition from locked to freely creeping in the downdip transition zone. We show that the locked zone at Cascadia is west of the coastline and 10 km updip of the slow slip zone along much of the margin, widest (25–125 km, extending to ∼19 km depth) in northern Cascadia, narrowest (0–70 km) in central Cascadia, with moment accumulation rate equivalent to a M_w 8.71 and M_w 8.85 earthquake for 300- and 500-year earthquake cycles. We find a steep gradient in creep immediately below the locked zone, indicative of propagating creep, along the entire margin. At Nankai, we find three distinct zones of locking (offshore Shikoku, offshore southeast Kii peninsula, and offshore Shima peninsula) with a total moment accumulation rate equivalent to a M_w 8.70 earthquake for a 150-year earthquake cycle. The bottom of the locked zone is nearly under the coastline for all three locked regions at Nankai and is positioned 0–5 km updip of the slow slip zone. In contrast with Cascadia, creep rate gradients below the locked zone at Nankai are generally gradual, consistent with stationary locking.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142490680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleomagnetic Field Variability and Revised Chronostratigraphy of Bering Sea (IODP Expedition 323) Deep-Sea Sediments During MIS 6–7 (130–144 ka)","authors":"Steve Lund,&nbsp;Emily Mortazavi,&nbsp;Joe Stoner,&nbsp;Makoto Okada","doi":"10.1029/2024JB029485","DOIUrl":"10.1029/2024JB029485","url":null,"abstract":"<div>\u0000 \u0000 \u0000 <section>\u0000 \u0000 <p>We have developed replicate paleomagnetic secular variation (PSV) records for MIS 6–7 (130–244 ka) from IODP Ex. 3 23 Sites 1,343, 1,344, and 1,345 (Bering Sea). We can correlate the PSV at all three sites and identify 90 inclination features and 64 declination features. We have developed relative paleointensity records for all three sites by normalizing the demagnetized natural remanence to magnetic susceptibility. Paleointensity highs/lows can be tied to the PISO-1500 global oxygen-isotope-dated paleointensity record. This provides a significant increase in chronostratigraphic resolution for these sites. Only one excursion is recorded in the MIS 6–7 sediments of the Bering Sea—the Iceland Basin Excursion (∼196 ± 3 ka). Replicate records of the inclinations and declinations both flip quickly to reversed polarity directions, stay there for several hundred years and then flip quickly back to normal polarity directions. However, the inclination flips occur without significant declinations changes and visa versa. A statistical PSV study was carried out by averaging the data in 3 ky and 9 ky windows. There is a distinctive bimodal pattern to the angular dispersions with most time spent with low angular dispersion values (∼10°–15°), but there is an interval of more than 30 ky (185–220 ka) with angular dispersions averaging two to three times higher amplitudes (∼25°–35°). This interval also has low paleointensities and the Iceland Basin Excursion. This same, coupled pattern of high angular dispersion, low paleointensity, and excursions is noted synchronously in the central North Atlantic Ocean and may indicate a global pattern to the geomagnetic field.</p>\u0000 </section>\u0000 </div>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142487750","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}