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ABSTRACT The Puerto Rico–Virgin Islands (PRVI) block lies within the Northern Caribbean Plate Boundary Zone—a zone accommodating stresses between the larger North America and Caribbean plates. Data from Global Positioning System (GPS) sites throughout the PRVI block have been used to confirm the existence of a distinct microblock in the southwest. It is no coincidence that this portion of the PRVI block is the epicentral region of the 7 January 2020 Mw 6.4 earthquake and the ensuing seismic sequence. Prior to the mainshock, the southwestern Puerto Rico (SWPR) region exhibited most of the onland seismic activity. The 2020–2021 SWPR earthquake seismic sequence has been characterized by having an atypical aftershock decay distribution occurring along multiple faults. As a result, fault parameters of the 7 January 2020 mainshock have been poorly defined by conventional seismic methods. Here, we present results from campaign and continuous GPS sites in SWPR, and compare GPS-derived displacements to those computed from the U.S. Geological Survey National Earthquake Information Center (NEIC) focal mechanism. We conclude that irrespective of which nodal plane is used, the observed coseismic displacements from GPS differ from those predicted using a simple elastic model and the NEIC focal mechanism. We infer based on these observations that the complex mainshock rupture resulted in a suboptimal double-couple solution.
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2020 Puerto Rico Earthquakes Field Assessment Structural Team Dataset:StEER - Puerto Rico Earthquake December 2019 to January 2020: Field Assessment Structural Team (FAST) Data Report
FAST deployed from 8-12 January 2020, documenting the performance of 61 structures located in six different cities along the southwestern coast of Puerto Rico between the cities of Ponce and Mayagüez. A variety of structure types are surveyed, including residential building structures and bridge infrastructures. FAST collected perishable data through the Fulcrum app by completing damage assessment forms, recording high-resolution overall and detailed images of observed damages, and notes summarizing key observations. Fieldwork data collection is conducted according to the StEER’s FAST handbook.This project encompasses the products of StEER's Level 2 response to the Puerto Rico Earthquake from December 2019 to January 2020. The main event, a Mw 6.4 quake, occurred on January 7th, accompanied by numerous aftershocks. The governor reported one casualty and eight injuries, declaring a State of Emergency. The earthquakes damaged 10,000+ structures, collapsing 80, predominantly residential units. Infrastructure, bridges, and roads were also affected, leaving two-thirds of the island without power. Over 8,000 people were displaced to shelters, while 63,000 received assistance, with FEMA handling over 13,852 aid requests. In response, the StEER conducted a post-earthquake performance assessment from 8-12 January 2020, documenting the performance of 60 structures located in six different cities along the southwestern coast of Puerto Rico. The field data collection focused on acquiring high-resolution photographs and notes on structural performance necessary to construct detailed case studies of each structure.
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- Award ID(s):
- 2103550
- PAR ID:
- 10513723
- Publisher / Repository:
- Designsafe-CI
- Date Published:
- Subject(s) / Keyword(s):
- Planning Documents Structural Assessments StEER - Structural Engineering Extreme Event Reconnaissance
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract A vigorous shallow earthquake sequence along the southern coast of Puerto Rico commenced on 28 December 2019 in a region with little prior large seismicity. The largest event in the sequence (MW = 6.4), struck on 7 January 2020 and involved normal faulting. It produced extensive damage in southern Puerto Rico and power disruption across the island. Nearby strong ground motions and static offsets from GPS stations along with teleseismic recordings are inverted for the kinematic rupture process of the mainshock. The ~15‐km‐long rupture is spatially concentrated, with most slip between 3 and 13 km deep and peak slip of ~1.6 m. The static stress drop is high, ~19 MPa, with the rupture locating in the eastern section of a ~30‐km‐long band of seismicity bisected by a near‐orthogonal lineation. Complex faulting and high stress in the intraplate region appears to be responsible for the high earthquake productivity.more » « less
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