When continental rifting is accompanied by localized magmatism under extensional stress, the breakup duration can be short and the continent/ocean transition sharp, as mantle melts are thought to be efficient at heating and weakening the lithosphere. This mode of rifting has been invoked for the Eastern North American Margin (ENAM) based on the existing geophysical data. Here, we present results from multichannel seismic profiles from the ENAM Community Seismic Experiment offshore North Carolina, U.S. Our survey area encompasses both the East Coast Magnetic Anomaly (ECMA) and the Blake Spur Magnetic Anomaly (BSMA), which lies ~200‐km farther seaward. Our prestack depth‐migrated seismic images reveal major changes in the structure of the igneous crust across the BSMA. Between the ECMA and BSMA, we image a proto‐oceanic domain of rough, faulted, and thin igneous crust. The roughness of this oceanic crust is similar to modern ultraslow spreading environments which involve the continued presence of a pre‐existing lithospheric lid. Seaward of the BSMA the basement is smooth, and the crust is relatively thick, which is typical for Jurassic oceanic crust. Across the BSMA, we image a step up in basement and crustal root, which we interpret to represent complete lithospheric breakup and a transition to steady‐state seafloor spreading in agreement with coincident refraction results. Our results would also indicate low extension rates in the final stages of rifting that may have influenced the thermal structure of the lithosphere and could explain the delay for continental breakup. All of these observations show that although continental rifting between eastern North America and northwest Africa was assisted by magmatic activity, it did not lead to rapid localization of extensional strain as previously thought.
- NSF-PAR ID:
- 10319291
- Date Published:
- Journal Name:
- Communications Earth & Environment
- Volume:
- 2
- Issue:
- 1
- ISSN:
- 2662-4435
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
Abstract As demonstrated at Anak Krakatau on December 22 nd , 2018, tsunamis generated by volcanic flank collapse are incompletely understood and can be devastating. Here, we present the first high-resolution characterisation of both subaerial and submarine components of the collapse. Combined Synthetic Aperture Radar data and aerial photographs reveal an extensive subaerial failure that bounds pre-event deformation and volcanic products. To the southwest of the volcano, bathymetric and seismic reflection data reveal a blocky landslide deposit (0.214 ± 0.036 km 3 ) emplaced over 1.5 km into the adjacent basin. Our findings are consistent with en-masse lateral collapse with a volume ≥0.175 km 3 , resolving several ambiguities in previous reconstructions. Post-collapse eruptions produced an additional ~0.3 km 3 of tephra, burying the scar and landslide deposit. The event provides a model for lateral collapse scenarios at other arc-volcanic islands showing that rapid island growth can lead to large-scale failure and that even faster rebuilding can obscure pre-existing collapse.more » « less
-
more » « less
Abstract Cities are the drivers of socioeconomic innovation and are also forced to address the accelerating risk of failure in providing essential services such as water supply today and in the future. Here, we investigate the resilience of urban water supply security, which is defined in terms of the services that citizens receive. The resilience of services is determined by the availability and robustness of critical system elements or “capitals” (water resources, infrastructure, finances, management efficacy, and community adaptation). We translate quantitative information about this portfolio of capitals from seven contrasting cities on four continents into parameters of a coupled system dynamics model. Water services are disrupted by recurring stochastic shocks, and we simulate the dynamics of impact and recovery cycles. Resilience emerges under various constraints, expressed in terms of each city's capital portfolio. Systematic assessment of the parameter space produces the urban water resilience landscape, and we determine the position of each city along a continuous gradient from water insecure and nonresilient to secure and resilient systems. In several cities stochastic disturbance regimes challenge steady‐state conditions and drive system collapse. While water insecure and nonresilient cities risk being pushed into a poverty trap, cities which have developed excess capitals risk being trapped in rigidity and crossing a tipping point from high to low services and collapse. Where public services are insufficient, community adaptation improves water security and resilience to varying degrees. Our results highlight the need for resilience thinking in the governance of urban water systems under global change pressures.
-
more » « less
Abstract Recollection bias (RB) refers to the phenomenon whereby after an adverse event people report that their risk assessment about a similar future event is presently no higher than their recollection of their pre‐event risk assessment. While previous research has outlined this theoretical construct and generated important empirical findings, there were some limitations. We design and employ a new national representative survey to address these limitations in this study. We examine the existence and persistence of RB among the general public in the context of a number of domestic and international terrorist attacks. We further examine the socioeconomic and political base of RB and the influences of RB on a wide range of citizens’ counterterrorism policy preferences. Our data analyses reveal strong evidence showing the occurrence of RB and its persistence across various forms of terrorism risk. With regard to the socioeconomic and political base, we find that females, older people, political conservatives, and Republicans are less likely to be subject to RB. For the effects of RB on public counterterrorism policy preferences, our analyses demonstrate that this bias significantly dampens public support for a wide range of preventive policy measures and government anti‐terrorism spending. Overall, our study, based on a national representative sample and an extended survey design, provides robust evidence of RB in terrorism risk assessment, and adds further evidence to support the idea that RB is likely a generalizable phenomenon. Implications and suggestions for future research are discussed in the conclusion.
-
more » « less
We respond as the Jakarta Collective to Prathiwi Putri’s constructive critique of Leitner and Sheppard’s research on Jakarta’s kampungs, to make visible the broader cluster of scholarship surrounding their research. Deploying six binaries, postcolonialism versus neoliberalism, non-capitalism versus capitalism, agency versus structure, displacement versus dispossession, and individual versus collective action, Putri suggests that Leitner and Sheppard stress the former while neglecting the latter. By taking the field seriously, we argue that the research of the Collective approaches these dialectically, teasing out their complex interrelations. Changes in Jakarta’s kampungs reflect its hybrid more-than-capitalist political economy, at the intersection of US and Chinese influence. The displacement of kampungs and kampung residents’ practices subsidize capitalism but they also contest its norms. Residents’ agency is significant; some gain but others lose, they act individually but also collectively. Highlighting more-than-capitalist practices opens up possibilities for alternative futures rather than simply documenting capitalist hegemony.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s43247-021-00284-7
