Seismic nests (or clusters) are typically defined as regions of high seismic activity at intermediate depths that do not move over time and are not associated with volcanic activity at the surface (e.g. Zarifi and Hayskov, 2003; Zarifi et al., 2007; Prieto et al., 2012). In this study, we focus on a seismic nest located in central Peru beneath the Amazon basin city of Pucallpa. The location of this nest is just beyond the eastern-most extent of the Peruvian flat slab, similar to the settings of two other South American clusters, the Bucaramanga and Pipanaco nests. While the Pucallpa nest is visible in the figures of many earlier papers on intermediate depth South American seismicity, it has not to our knowledge been described as a seismic nest before. We present the first detailed description of the Pucallpa nest, compare it to other established nests, and discuss its implications for our understanding of the Peruvian flat slab. Our results indicate that the Pucallpa nest demarcates the northern margin of a sag in the horizontally subducting Nazca plate in central Peru. The position of the nest along the projected location of the downgoing Mendana fracture zone is consistent with local variations in b-values and could help to explain both the nest's genesis and the co-located change in slab geometry. The nest is also spatially well correlated with the northern margin of the thick-skinned Shira Mountains and with the high heat flow associated with the Agua Caliente dome (Hermoza et al., 2006; Navarro Comet, 2018). Further study is needed to understand the effects of the complex Peruvian slab geometry on the formation of thick skinned deformation and heat flow anomalies on the overriding South American continent.

Seismic nests (or clusters) are typically defined as regions of high seismic activity at intermediate depths that do not move over time and are not associated with volcanic activity at the surface (e.g. Zarifi and Hayskov, 2003; Zarifi et al., 2007; Prieto et al., 2012). In this study, we focus on a seismic nest located in central Peru beneath the Amazon basin city of Pucallpa. The location of this nest is just beyond the eastern-most extent of the Peruvian flat slab, similar to the settings of two other South American clusters, the Bucaramanga and Pipanaco nests. While the Pucallpa nest is visible in the figures of many earlier papers on intermediate depth South American seismicity, it has not to our knowledge been described as a seismic nest before. We present the first detailed description of the Pucallpa nest, compare it to other established nests, and discuss its implications for our understanding of the Peruvian flat slab. Our results indicate that the Pucallpa nest demarcates the northern margin of a sag in the horizontally subducting Nazca plate in central Peru. The position of the nest along the projected location of the downgoing Mendana fracture zone is consistent with local variations in b-values and could help to explain both the nest's genesis and the co-located change in slab geometry. The nest is also spatially well correlated with the northern margin of the thick-skinned Shira Mountains and with the high heat flow associated with the Agua Caliente dome (Hermoza et al., 2006; Navarro Comet, 2018). Further study is needed to understand the effects of the complex Peruvian slab geometry on the formation of thick skinned deformation and heat flow anomalies on the overriding South American continent.

The eastern North American margin community seismic experiment (ENAM-CSE) was conceived to target the ENAM Geodynamic Processes at Rifting and Subducting Margins (GeoPRISMS) primary site with a suite of both active- and passive-source seismic data that would shed light on the processes associated with rift initiation and evolution. To fully understand the ENAM, it was necessary to acquire a seismic dataset that was both amphibious, spanning the passive margin from the continental interior onto the oceanic portion of the North American plate, and multiresolution, enabling imaging of the sediments, crust, and mantle lithosphere. The ENAM-CSE datasets were collected on- and offshore of North Carolina and Virginia over a series of cruises and land-based deployments between April 2014 and June 2015. The passive-source component of the ENAM-CSE included 30 broadband ocean-bottom seismometers (OBSs) and 3 onshore broadband instruments. The broadband stations were deployed contemporaneously with those of the easternmost EarthScope Transportable Array creating a trans-margin amphibious seismic dataset. The active-source portion of the ENAM-CSE included several components: (1) two onshore wide-angle seismic profiles where explosive shots were recorded on closely spaced geophones; (2) four major offshore wide-angle seismic profiles acquired with an airgun source and short-period OBSs (SPOBSs), two of which were extended onland by deployments of short-period seismometers; (3) marine multichannel seismic (MCS) data acquired along the four lines of SPOBSs and a series of other profiles along and across the margin. During the cruises, magnetic, gravity, and bathymetric data were also collected along all MCS profiles. All of the ENAM-CSE products were made publicly available shortly after acquisition, ensuring unfettered community access to this unique dataset.

The eastern North American margin community seismic experiment (ENAM-CSE) was conceived to target the ENAM Geodynamic Processes at Rifting and Subducting Margins (GeoPRISMS) primary site with a suite of both active- and passive-source seismic data that would shed light on the processes associated with rift initiation and evolution. To fully understand the ENAM, it was necessary to acquire a seismic dataset that was both amphibious, spanning the passive margin from the continental interior onto the oceanic portion of the North American plate, and multiresolution, enabling imaging of the sediments, crust, and mantle lithosphere. The ENAM-CSE datasets were collected on- and offshore of North Carolina and Virginia over a series of cruises and land-based deployments between April 2014 and June 2015. The passive-source component of the ENAM-CSE included 30 broadband ocean-bottom seismometers (OBSs) and 3 onshore broadband instruments. The broadband stations were deployed contemporaneously with those of the easternmost EarthScope Transportable Array creating a trans-margin amphibious seismic dataset. The active-source portion of the ENAM-CSE included several components: (1) two onshore wide-angle seismic profiles where explosive shots were recorded on closely spaced geophones; (2) four major offshore wide-angle seismic profiles acquired with an airgun source and short-period OBSs (SPOBSs), two of which were extended onland by deployments of short-period seismometers; (3) marine multichannel seismic (MCS) data acquired along the four lines of SPOBSs and a series of other profiles along and across the margin. During the cruises, magnetic, gravity, and bathymetric data were also collected along all MCS profiles. All of the ENAM-CSE products were made publicly available shortly after acquisition, ensuring unfettered community access to this unique dataset.

The border between Georgia and South Carolina has a moderate amount of seismicity typical of the Piedmont Province of the eastern United States and greater than most other intraplate regions. Historical records suggest on average a M-w 4.5 earthquake every 50 yr in the region of the J. Strom Thurmond Reservoir, which is located on the border between Georgia and South Carolina. The M-w 4.1 earthquake on 15 February 2014 near Edgefield, South Carolina, was one of the largest events in this region recorded by nearby modern seismometers, providing an opportunity to study its source properties and aftershock productivity. Using the waveforms of the M-w 4.1 mainshock and the only cataloged M w 3.0 aftershock as templates, we apply a matched-filter technique to search for additional events between 8 and 22 February 2014. The resulting six new detections are further employed as new templates to scan for more events. Repeating the waveform-matching method with new templates yields 13 additional events, for a total of 19 previously unidentified events with magnitude 0.06 and larger. The low number of events suggests that this sequence is deficient in aftershock production, as compared with expected aftershock productivities for other mainshocks of similar magnitudes. Hypocentral depths of the M-w 4.1 mainshock and M-w 3.0 aftershock are estimated by examining the differential time between a depth phase called sPL and P-wave arrivals, as well as by modeling the depth phase of body waves at shorter periods. The best-fitting depths for both events are around 3-4 km. The obtained stress drops for the M-w 4.1 mainshock and M-w 3.0 aftershock are 3.75 and 4.44 MPa, respectively. The corresponding updated moment magnitude for the aftershock is 2.91.