Two parallel trench-normal fault planes within the Pacific slab associated with the 1994 and 2000 Kurile earthquakes as revealed by simultaneous relocation of their main shocks and aftershocks

The Cretaceous igneous rocks in the South China Block (SCB) were associated with the slab subduction and roll-back of the Pacific Plate. Thus, they provide excellent opportunities to examine the spatial–temporal geochemical migration of magmatism in the retreating subduction margins. The Cretaceous mafic–intermediate igneous rocks from the southeastern SCB were aged between 142 and 71 Ma, and can geochemically be subdivided into three groups: Group A (126–129 Ma and 83–93 Ma), Group B (126–142 Ma and 71–108 Ma) and Group C (116–142 Ma and 70–110 Ma). Group A and B were mainly distributed in the SCB interior and derived from asthenosphere and asthenosphere–lithosphere interaction sources, respectively. Group C occurred to the east of the Ganjiang Fault and originated from slab–lithosphere interaction. From the coastal provinces to the interior, these mafic–intermediate igneous rocks show increasing incompatible element ratios and Nd isotopic compositions, reflective of a westerly decreasing involvement of slab-derived components. They show two similar age-pulses at c. 125 Ma and c. 90 Ma as well as the Cretaceous A-type granites, indicating two episodes of subduction retreat of the Pacific slab during the Cretaceous. This spatial–temporal pattern of the Cretaceous mafic–intermediate igneous rocks suggests that the Cretaceous slab metasomatism of Pacific subduction retreat was limited to the east of the Ganjiang Fault.Supplementary material: Tables of geochemical data and additional figures are available at https://doi.org/10.6084/m9.figshare.c.4938576

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Recent instrumental seismicity of the southwest Matese Massif (Sannio-Matese area - Italy): a contribution on the seismotectonics setting.

10.5194/egusphere-egu2020-15851 ◽

2020 ◽

Author(s):

Girolamo Milano

Keyword(s):

Fault Plane ◽

Normal Fault ◽

Focal Mechanisms ◽

Common Element ◽

Mountain Range ◽

Depth Range ◽

Main Shocks ◽

Southern Side ◽

A Minor ◽

Low Magnitude

The Matese Massif is the major mountain range of the Sannio-Matese, which is the transition area between central and southern Apennines. The Massif is located among the seismogenic sources of large destructive historical Earthquakes (e.g. 1349, MW =7.0; 1688, MW = 6.6; 1805, MW = 6.8). Previous studies on the instrumental seismicity of the Sannio-Matese have shown that the seismic activity along and close to the Matese Massif is prevalently characterized by the occurrence of sparse low magnitude events (ML<2.5) and by seismic sequences with low to moderate magnitude (MWmax=5.0) with hypocenters within the uppermost crust. Last relevant seismic sequence occurred between the late 2013-early 2014 following an MW=5.0 earthquake. This sequence struck the internal southern side of the Massif in an area where no evidence of active faulting has been recorded so far. Multidisciplinary investigation on this sequence suggest that the sequence has developed along a SW dipping NNW-SSE striking normal fault, ~10 km long, confined in the 10-20 km depth range. The 1805 Earthquake affected the northern slope of the Massif whereas the 1349 and 1688 Earthquakes affected the southern side. The 1349 Earthquake, that includes at least three main shocks, given its age, stands out due to the lack of reliable and sufficiently vast historical documentation. Geological, geomorphological and historical analysis on this Earthquake evidenced a SW dipping 125 striking 22 km length normal fault, named Aquae Iuliae Fault (AIF), as responsible for one of the main shocks of this Earthquake. In order to provide further information on the seismotectonics setting of the southwest sector of the Matese Massif, here is analyzed the instrumental seismicity occurred in 2009-2019 time interval in the area of the 1349 Earthquake. The spatial distribution of the relocated seismicity mainly consists of single events with magnitude ML&#8804;3.5. The single events are localized prevalently nearby AIF and have foci falling generally in the first 15 km of the crust. The focal mechanisms of the most energetic events show normal dip-slip solutions, with NW-SE striking planes and NE-SW striking T-axes. The epicentral distribution of a low magnitude seismic swarm, triggered by an earthquake of ML 3.3 and constituted by about 120 events,&#160; shows a roughly WNW-ESE alignment. The hypocenters, confined in the range 5-15 km depth, roughly depict a SW dipping plane. The fault plane solutions of the very few events of this swarm with ML > 2.0 show both normal dip slip solutions, with a minor strike component, and strike-slip solutions, with a minor dip component. The common element of these focal mechanisms is the presence of a SW dipping fault plane, striking from NW-SE to NNW-SSE. The preliminary results of this study, taking into account the dipping plane of the 2013-2014 sequence and that of the AIF, suggest that the release of seismic energy in the southwest side of the Matese Massif occur on very small fault segments, with SW dipping.

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Seismic anisotropy of the Pacific slab and mantle wedge beneath the Japanese islands

Journal of Geophysical Research Atmospheres ◽

10.1029/2009jb006290 ◽

2009 ◽

Vol 114 (B7) ◽

Cited By ~ 22

Author(s):

Yoko Tono ◽

Yoshio Fukao ◽

Takashi Kunugi ◽

Seiji Tsuboi

Keyword(s):

Mantle Wedge ◽

Seismic Anisotropy ◽

The Pacific ◽

Pacific Slab ◽

Japanese Islands

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Seismicity characterization of oceanic earthquakes in the Mexican territory

10.5194/se-2019-180 ◽

2020 ◽

Author(s):

Quetzalcoatl Rodríguez-Pérez ◽

Víctor Hugo Márquez-Ramírez ◽

Francisco Ramón Zúñiga

Keyword(s):

Normal Fault ◽

B Value ◽

Statistical Characteristics ◽

P Value ◽

Transform Faults ◽

Frequency Distributions ◽

Ocean Ridges ◽

The Pacific ◽

Stress Orientations ◽

Clear Differentiation

Abstract. We analyzed the seismicity of oceanic earthquakes in the Pacific oceanic regime of Mexico. We used data from the earthquake catalogs of the Mexican National Service (SSN), and the International Seismological Center (ISC) from 1967 to 2017. Events were classified into two different categories: intraplate oceanic (INT), and transform faults zone and mid-ocean ridges events (TF-MOR), respectively. For each category, we determined statistical characteristics such as magnitude frequency distributions, the aftershocks decay rate, the non-extensivity parameters, and the regional stress field. We obtained b-values of 1.17, and 0.82 for the INT, and TF-MOR events, respectively. TF-MOR events also exhibit local b-value variations in the range of 0.72–1.30. TF-MOR events follow a tapered Gutenberg-Richter distribution. We also obtained a p-value of 0.67 for the 1 May 1997 (Mw = 6.9) earthquake. By analyzing the non-extensivity parameters, we obtained similar q-values in the range of 1.39–1.60 for both types of earthquakes. On the other hand, the parameter a showed a clear differentiation, being higher for TF-MOR events than for INT events. This implies that more energy is released for TF-MOR events. Stress orientations are in agreement with geodynamical models for transform faults zone and mid-ocean ridges zones. In the case of intraplate seismicity, stresses are mostly related to a normal fault regime.

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P-wave attenuation in the Pacific slab beneath northeastern Japan revealed by the spectral ratio of intraslab earthquakes

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2018.02.032 ◽

2018 ◽

Vol 489 ◽

pp. 37-48 ◽

Cited By ~ 3

Author(s):

Takahiro Shiina ◽

Junichi Nakajima ◽

Toru Matsuzawa

Keyword(s):

Wave Attenuation ◽

Spectral Ratio ◽

P Wave ◽

Northeastern Japan ◽

The Pacific ◽

Pacific Slab

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Heterogeneous Behavior of the Campotosto Normal Fault (Central Italy) Imaged by InSAR GPS and Strong-Motion Data: Insights from the 18 January 2017 Events

Remote Sensing ◽

10.3390/rs11121482 ◽

2019 ◽

Vol 11 (12) ◽

pp. 1482 ◽

Cited By ~ 5

Author(s):

Daniele Cheloni ◽

Nicola D’Agostino ◽

Laura Scognamiglio ◽

Elisa Tinti ◽

Christian Bignami ◽

...

Keyword(s):

Central Italy ◽

Sampling Rate ◽

Strong Motion ◽

Normal Fault ◽

Slip Distribution ◽

Fault System ◽

Time Interval ◽

Seismic Sequence ◽

Main Shocks ◽

Heterogeneous Behavior

On 18 January 2017, the 2016–2017 central Italy seismic sequence reached the Campotosto area with four events with magnitude larger than 5 in three hours (major event MW 5.5). To study the slip behavior on the causative fault/faults we followed two different methodologies: (1) we use Interferometric Synthetic Aperture Radar (InSAR) interferograms (Sentinel-1 satellites) and Global Positioning System (GPS) coseismic displacements to constrain the fault geometry and the cumulative slip distribution; (2) we invert near-source strong-motion, high-sampling-rate GPS waveforms, and high-rate GPS-derived static offsets to retrieve the rupture history of the two largest events. The geodetic inversion shows that the earthquake sequence occurred along the southern segment of the SW-dipping Mts. Laga normal fault system with an average slip of about 40 cm and an estimated cumulative geodetic moment of 9.29 × 1017 Nm (equivalent to a MW~6). This latter estimate is larger than the cumulative seismic moment of all the events, with MW > 4 which occurred in the corresponding time interval, suggesting that a fraction (~35%) of the overall deformation imaged by InSAR and GPS may have been released aseismically. Geodetic and seismological data agree with the geological information pointing out the Campotosto fault segment as the causative structure of the main shocks. The position of the hypocenters supports the evidence of an up-dip and northwestward rupture directivity during the major shocks of the sequence for both static and kinematic inferred slip models. The activated two main slip patches are characterized by rise time and peak slip velocity in the ranges 0.7–1.1 s and 2.3–3.2 km/s, respectively, and by ~35–50 cm of slip mainly concentrated in the shallower northern part of causative fault. Our results show that shallow slip (depth < 5 km) is required by the geodetic and seismological observations and that the inferred slip distribution is complementary with respect to the previous April 2009 seismic sequence affecting the southern half of the Campotosto fault. The recent moderate strain-release episodes (multiple M~5–5.5 earthquakes) and the paleoseismological evidence of surface-rupturing events (M~6.5) suggests therefore a heterogeneous behavior of the Campotosto fault.

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Paleoseismicity, Ecological Change, and Prehistoric Exploitation of Anadromous Fishes in the Salmon River Basin, Western Idaho, USA

North American Archaeologist ◽

10.2190/na.28.3.b ◽

2007 ◽

Vol 28 (3) ◽

pp. 233-263 ◽

Cited By ~ 3

Author(s):

Loren G. Davis

Keyword(s):

Native American ◽

Pacific Northwest ◽

River Basin ◽

Normal Fault ◽

Ecological Change ◽

Salmon River ◽

The Pacific ◽

Fluvial Response ◽

Induced Changes ◽

Salmon Fishery

By the middle Holocene, Native American groups developed semi-sedentary villages in the Columbia River basin of the Pacific Northwest. The economic basis for these villages is thought to have been predicated on the acquisition of bulk food resources, such as salmon and camas, for delayed consumption during the winter. In Idaho's lower Salmon River canyon, semi-sedentary pit house villages are absent until after 2000 14C yr BP. Floodplain geochronology shows channel incision and terrace formation occurred at ca. 2000 14C yr BP, caused by fluvial response to neotectonic displacement along a normal fault. The delayed appearance of pit house sites and other markers of the Winter Village Pattern in the canyon is argued to be directly related to neotectonically-induced changes in fluvial conditions after 2000 14C yr BP, which significantly improved aquatic habitats for anadromous fishes and led to the development of a predictable, productive salmon fishery.

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