The 1997 Umbria-Marche (Italy) earthquake sequence: Relationship between ground deformation and seismogenic structure

SUMMARY Tectonic slivers form in the overriding plate in regions of oblique subduction. The inner boundaries of the sliver are often poorly defined and can consist of well-defined faults, rotating blocks or diffuse fault systems, which pass through or near the volcanic arc. The Guanacaste Volcanic Arc Sliver (GVAS) as defined by Montero et al., is a segment of the Central American Forearc Sliver, whose inner boundary is the ∼87-km-long Haciendas-Chiripa fault system (HCFS), which is located ∼10 km behind the volcanic arc and consists of strike slip faults and pull apart steps. We characterize the current ground motion on this boundary by combining earthquake locations and focal mechanisms of the 2016 Bijagua earthquake sequence, with the surface ground deformation obtained from Interferometric Synthetic Aperture Radar (InSAR) images from the ALOS-2 satellite. The coseismic stack of interferograms show ∼6 cm of displacement towards the line of sight of the satellite between the Caño Negro fault and the Upala fault, indicating uplift or SE horizontal surface displacement. The largest recorded earthquake of the sequence was Mw 5.4, and the observed deformation is one of the smallest earthquakes yet detected by InSAR in the Central American region. Forward and inverse models show the surface deformation can be partially explained by slip on a single fault, but it can be better explained by slip along two faults linked at depth. The best-fitting model consists of 0.33 m of right lateral slip on the Caño Negro fault and 0.35 m of reverse slip on the Upala fault, forming a positive flower structure. As no reverse seismicity was recorded, we infer the slip on the Upala fault occurred aseismically. Observations of the Bijagua earthquake sequence suggests the forearc sliver boundary is a complex and diffuse fault system. There are localized zones of transpression and transtension and areas where there is no surface expression suggesting the fault system is not yet mature. Although aseismic slip is common on subduction interfaces and mature strike-slip faults, this is the first study to document aseismic slip on a continental tectonic sliver boundary fault.

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A more accurate relocation of the 2013 M s7.0 Lushan, Sichuan, China, earthquake sequence, and the seismogenic structure analysis

Journal of Seismology ◽

10.1007/s10950-015-9485-0 ◽

2015 ◽

Vol 19 (3) ◽

pp. 653-665 ◽

Cited By ~ 8

Author(s):

F. Long ◽

X. Z. Wen ◽

X. Ruan ◽

M. Zhao ◽

G. X. Yi

Keyword(s):

Structure Analysis ◽

Earthquake Sequence ◽

Seismogenic Structure ◽

China Earthquake

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Focal Mechanism and Seismogenic Structure of the MS 5.1 Qingbaijiang Earthquake on February 3, 2020, Southwestern China

Frontiers in Earth Science ◽

10.3389/feart.2021.644142 ◽

2021 ◽

Vol 9 ◽

Author(s):

Min Zhao ◽

Feng Long ◽

Guixi Yi ◽

MingJian Liang ◽

Jiangtao Xie ◽

...

Keyword(s):

Fault Zone ◽

Focal Mechanism ◽

Earthquake Sequence ◽

Southwestern China ◽

Joint Analysis ◽

Focal Mechanism Solution ◽

Inversion Method ◽

Seismogenic Structure ◽

Initial Rupture ◽

Hypocentral Distribution

The 3 February 2020 MS 5.1 Qingbaijiang earthquake, southwestern China, is the closest recorded MS ≥ 5.0 event to downtown Chengdu City to date, with an epicentral distance of only 38 km. Here we analyze seismic data from the Sichuan and Chengdu regional seismic networks, and employ a multi-stage location method to relocate the earthquakes that have occurred along the central and northern segments of the Longquanshan fault zone since 2009, including the MS 5.1 Qingbaijiang earthquake sequence, to investigate the seismogenic structure of the region. The relocation results indicate that the seismicity along the central and northern segments of the Longquanshan fault zone has occurred mainly along the eastern branch since 2009, with the hypocentral distribution along a vertical cross-section illustrating a steep, NW-dipping parallel imbricate structure. The terminating depth of the eastern branch is about 12 km. The distribution of the MS 5.1 Qingbaijiang earthquake sequence is along the NE–SW-striking Longquanshan fault zone. The aftershock focal depths are in the 3–6 km range, with the mainshock located at 104.475°E, 30.73°N. Its initial rupture depth of 5.2 km indicates that the earthquake occurred above the shallow decollement layer of the upper crust in this region. The hypocentral distribution along the long axis of the aftershock area highlights that this earthquake sequence occurred along a fault dipping at 56° to the NW. Our surface projection of the inferred fault plane places it near the eastern branch of the Longquanshan fault zone. We infer the MS 5.1 mainshock to be a thrust faulting event based on the focal mechanism solution via the cut-and-paste waveform inversion method, with strike/dip/rake parameters of 22°/36°/91° and 200°/54°/89° obtained for nodal planes I and II, respectively. We identify that the seismogenic fault of the MS 5.1 Qingbaijiang earthquake lies along the eastern branch of the Longquanshan fault zone, and nodal plane II represents the coseismic rupture plane, based on a joint analysis of the event relocation results, mainshock focal mechanism, and regional geological information. Our study provides vital information for assessing the seismic hazard of the Longquanshan fault zone near Chengdu City.

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Documentation of Surface Fault Rupture and Ground-Deformation Features Produced by the 4 and 5 July 2019 Mw 6.4 and Mw 7.1 Ridgecrest Earthquake Sequence

Seismological Research Letters ◽

10.1785/0220190322 ◽

2020 ◽

Vol 91 (5) ◽

pp. 2942-2959 ◽

Cited By ~ 10

Author(s):

Daniel J. Ponti ◽

James Luke Blair ◽

Carla M. Rosa ◽

Kate Thomas ◽

Alexandra J. Pickering ◽

...

Keyword(s):

Slope Failure ◽

Ground Deformation ◽

Field Measurements ◽

Earthquake Hazard ◽

Earthquake Sequence ◽

Digital Data ◽

Fault Rupture ◽

Ground Failure ◽

Eastern California Shear Zone ◽

Deformation Features

Abstract The Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence occurred on 4 and 5 July 2019 within the eastern California shear zone of southern California. Both events produced extensive surface faulting and ground deformation within Indian Wells Valley and Searles Valley. In the weeks following the earthquakes, more than six dozen scientists from government, academia, and the private sector carefully documented the surface faulting and ground-deformation features. As of December 2019, we have compiled a total of more than 6000 ground observations; approximately 1500 of these simply note the presence or absence of fault rupture or ground failure, but the remainder include detailed descriptions and other documentation, including tens of thousands of photographs. More than 1100 of these observations also include quantitative field measurements of displacement sense and magnitude. These field observations were supplemented by mapping of fault rupture and ground-deformation features directly in the field as well as by interpreting the location and extent of surface faulting and ground deformation from optical imagery and geodetic image products. We identified greater than 68 km of fault rupture produced by both earthquakes as well as numerous sites of ground deformation resulting from liquefaction or slope failure. These observations comprise a dataset that is fundamental to understanding the processes that controlled this earthquake sequence and for improving earthquake hazard estimates in the region. This article documents the types of data collected during postearthquake field investigations, the compilation effort, and the digital data products resulting from these efforts.

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Source Parameters of the 2014Ms 6.5 Ludian Earthquake Sequence and Their Implications on the Seismogenic Structure

Seismological Research Letters ◽

10.1785/0220150085 ◽

2015 ◽

Vol 86 (6) ◽

pp. 1614-1621 ◽

Cited By ~ 8

Author(s):

Zujun Xie ◽

Yong Zheng ◽

Chengli Liu ◽

Xiong Xiong ◽

Yongdong Li ◽

...

Keyword(s):

Source Parameters ◽

Earthquake Sequence ◽

Seismogenic Structure ◽

Ludian Earthquake

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Relocation and seismogenic structure of the 1998 Zhangbei-Shangyi earthquake sequence

Acta Seismologica Sinica ◽

10.1007/s11589-002-0031-0 ◽

2002 ◽

Vol 15 (4) ◽

pp. 383-394 ◽

Cited By ~ 7

Author(s):

Zhi-xian Yang ◽

Yun-tai Chen ◽

Hong-zhi Zhang

Keyword(s):

Earthquake Sequence ◽

Seismogenic Structure

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Ground Deformation Data from GEER Investigations of Ridgecrest Earthquake Sequence

Seismological Research Letters ◽

10.1785/0220190291 ◽

2020 ◽

Vol 91 (4) ◽

pp. 2024-2034 ◽

Cited By ~ 7

Author(s):

Scott J. Brandenberg ◽

Jonathan P. Stewart ◽

Pengfei Wang ◽

Chukwuebuka C. Nweke ◽

Kenneth Hudson ◽

...

Keyword(s):

Ground Deformation ◽

Point Clouds ◽

Earthquake Sequence ◽

Digital Cameras ◽

Fault Rupture ◽

Ground Deformations ◽

Measuring Devices ◽

Surface Models ◽

Data Products ◽

Aerial Vehicle

Abstract Following the Ridgecrest earthquake sequence, consisting of an M 6.4 foreshock and M 7.1 mainshock along with many other events, the Geotechnical Extreme Events Reconnaissance association deployed a team to gather perishable data. The team focused their efforts on documenting ground deformations including surface fault rupture south of the Naval Air Weapons Station China Lake, and liquefaction features in Trona and Argus. The team published a report within two weeks of the M 7.1 mainshock. This article presents data products gathered by the team, which are now published and publicly accessible. The data products presented herein include ground-based observations using Global Positioning System trackers, digital cameras, and hand-measuring devices, as well as unmanned aerial vehicle-based imaging products using Structure from Motion to create point clouds and digital surface models. The article describes the data products, as well as tools available for interacting with the products.

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