scholarly journals Recognition of Pleistocene marine terraces in the southwest of Portugal (Iberian Peninsula): evidences of regional Quaternary uplift

2014 ◽  
Vol 56 (6) ◽  
Author(s):  
Paula M. Figueiredo ◽  
João Cabral ◽  
Thomas K. Rockwell
Keyword(s):  
Plate Boundary ◽  
Historical Earthquakes ◽  
Tectonic Activity ◽  
Sedimentary Deposits ◽  
Active Structures ◽  
Mainland Portugal ◽  
Marine Terraces ◽  
Moderate Seismicity ◽  
Beach Sediments ◽  
Sea Cliffs

<p>Southwest mainland Portugal is located close to the Eurasia-Nubia plate boundary and is characterized by moderate seismicity, although strong events have occurred as in 1755 (Mw≥8), 1969, (Mw 7.9), and more recently in 2007 (Mw 5.9) and 2009 (Mw 5.5), all located in the offshore. No historical earthquakes with onshore rupture are known for this region. At the coastline, high sea cliffs, incised drainages, emergent marine abrasion platforms and paleo sea cliffs indicate that this region is undergoing uplift, although no morphological features were found that could be unequivocally associated with the 1755 mega earthquake. To better understand the recent tectonic activity in this sector of Iberia, it is necessary not only to analyze active structures on land, but also to search for evidence for deformation that may relate to inferred offshore active structures. We thus conducted a study of marine terraces along the coastline to identify regional vertical crustal motions. Several poorly preserved surfaces with thin sedimentary deposits, comprising old beach sediments, were recognized at elevations starting at 2 m elevation and rising inland up to a regional abrasion platform situated at about 120 m a.s.l.. We identified distinct paleo sea level references at several locations at consistent elevations. This terrace sequence is likely Late Pleistocene in age, with individual platforms correlative to MIS 5 high stands and is coherent with a long-term slow uplift of the littoral zone for the southwest of Portugal. Although dating of discrete platforms is an ongoing and difficult task, preliminary correlations of paleo-shoreline elevations suggest that the uplift rate is in the range of 0.1-0.2 mm/yr.</p>

Surface deformation deduced from CGPS data in the eastern Betic External Zones (SE Spain). Implications on SHA

2020 ◽  
Author(s):  
Ivan Martin-Rojas ◽  
Alberto Sánchez-Alzola ◽  
Ivan Medina-Cascales ◽  
Maria Jose Borque ◽  
Pedro Alfaro ◽  
...  
Keyword(s):  
Surface Deformation ◽  
Plate Boundary ◽  
Historical Earthquakes ◽  
Betic Cordillera ◽  
Active Deformation ◽  
Active Structure ◽  
Plate Convergence ◽  
The North ◽  
Moderate Seismicity ◽  
Shortening Rate

&lt;p&gt;The Betic Cordillera (S Spain), located in the convergent plate boundary between Eurasia and Nubia, is an area of moderate seismicity. These plates converge at a rate of approximately 4 to 6 mm/yr in the NW-SE direction (see review by Nocquet, 2012). Between 2.7 to 3.9 mm/yr of present-day plate convergence is accommodated in N Africa. Active shortening must occur at rates ranging from 1.6 to 2.7&amp;#177;0.6 mm/year across the Algero-Balearic Basin and the SE Iberian Peninsula (Serpelloni et al., 2007; P&amp;#233;rez-Pe&amp;#241;a et al., 2010; Echeverr&amp;#237;a et al., 2013). In the Betic Cordillera, most of the deformation is concentrated in the Betic Internal Zones, while the Betic External zones are considered as a slow-strain area.&lt;/p&gt;&lt;p&gt;In SE of Spain onshore active deformation and seismicity are mainly located along the Eastern Betic Shear Zone (EBSZ), a major strike-slip tectonic corridor belonging to the Betic Internal Zones. Regional and local geodetic studies indicate that the EBSZ is absorbing between 0.2 and 1.3 mm/yr (Serpelloni et al., 2007; P&amp;#233;rez-Pe&amp;#241;a et al., 2010; Echeverr&amp;#237;a et al., 2013; Borque et al., 2019), i.e. only a portion of regional deformation. We postulate that part of this deformation not absorbed by the EBSZ is accommodated in the eastern Betic External Zones, located to the north of the EBSZ, where several major historical earthquakes occurred (e.g., the 1748 Estubeny, 1396 Tavernes, and 2017 Caudete earthquakes). These major events have been attributed to the Jumilla Fault, the only major active structure described in this area (Giner-Robles et al. 2014; Garc&amp;#237;a-Mayordomo, J. and Jim&amp;#233;nez-D&amp;#237;az, A., 2015).&lt;/p&gt;&lt;p&gt;We present new CGPS data analysis that corroborate that the eastern Betic External Zones accommodate a significant part of the present convergence. Furthermore, our preliminary data quantify deformation in this area for the first time, as we obtain a shortening rate in the N-S direction of 1.43&amp;#177;0.06 mm/yr in the western sector of the Jumilla Fault (Murcia sector) and of 1.69&amp;#177;0.07 mm/yr in the eastern sector of the fault (Valencia sector). We propose that this deformation is likely related to the Jumilla Fault. Our study place constraints on the seismic potential of the highly populated eastern Betic External Zones, as the preliminary values that we obtained are significantly higher than those previously stated. Consequently, we propose that a re-assesment of seismic hazard is necessary for this highly populated region. Moreover, we also propose a regional geodynamic model that provide insights into mechanisms controlling earthquakes in the eastern Betic External Zones.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Borque et al. (2019). Tectonics, 38, 5, 1824-1839&lt;/p&gt;&lt;p&gt;Echeverria et al. (2013). Tectonophysics, 608, 600-612.&lt;/p&gt;&lt;p&gt;Giner-Robles et al. (2014). Res&amp;#250;menes de la 2&amp;#170; Reuni&amp;#243;n Ib&amp;#233;rica sobre Fallas Activas y Paleosismolog&amp;#237;a, Lorca, Espa&amp;#241;a, 155-158.&lt;/p&gt;&lt;p&gt;Garc&amp;#237;a-Mayordomo, J. and Jim&amp;#233;nez-D&amp;#237;az, A. (2015). In: Quaternary Faults Database of Iberia v.3.0 - November 2015 (Garc&amp;#237;a-Mayordomo et al., eds.), IGME, Madrid.&lt;/p&gt;&lt;p&gt;Nocquet, J.M. (2012). Tectonophysics, 579, 220-242.&lt;/p&gt;&lt;p&gt;P&amp;#233;rez-Pe&amp;#241;a et al. (2010). Geomorphology, 119, 74-87&lt;/p&gt;&lt;p&gt;Serpelloni et al. (2007). Geophysical Journal Internationl, 169(3), 1180-1200.&lt;/p&gt;

Marine Terraces Reveal Complex Near-Shore Upper-Plate Faulting in the Northern Hikurangi Margin, New Zealand

2020 ◽  
Vol 110 (2) ◽  
pp. 825-849 ◽  
Author(s):  
Nicola J. Litchfield ◽  
Kate J. Clark ◽  
Ursula A. Cochran ◽  
Alan S. Palmer ◽  
Joshu Mountjoy ◽  
...  
Keyword(s):  
New Zealand ◽  
Plate Boundary ◽  
River Mouth ◽  
Seismic Reflection Data ◽  
Subduction Earthquakes ◽  
Reflection Data ◽  
Marine Terraces ◽  
Need To Evaluate ◽  
Near Shore ◽  
Recent Earthquakes

ABSTRACT Recent earthquakes involving multiple fault ruptures highlight the need to evaluate complex coastal deformation mechanisms, which are important for understanding plate boundary kinematics and seismic and tsunami hazards. We compare ages and uplift of the youngest Holocene marine terraces at Puatai Beach and Pakarae River mouth (∼10  km apart) in the northern Hikurangi subduction margin to examine whether uplift is the result of subduction earthquakes or upper-plate fault earthquakes. From stepped platform-cliff morphology, we infer uplift during 2–3 earthquakes and calculate an average uplift-per-event of 2.9±0.5  m at Puatai Beach and 2.0±0.5  m at Pakarae River mouth. Radiocarbon ages from the youngest beach deposit shells on each terrace and a tephra coverbed on one terrace constrain the timing of earthquakes to 1770–1710, 1100–910, and 420–250 cal. B.P. at Puatai Beach, and 1490–1290 and 660–530 cal. B.P. at Pakarae River mouth. The ages differ at each site indicating uplift is neither the result of subduction earthquakes nor single upper-plate fault earthquakes. A reinterpretation of new and existing bathymetry and seismic reflection data, combined with dislocation modeling, indicates that near-shore fault segmentation is more complex than previously thought and ruptures likely involve multiple upper-plate faults. Future updates of the New Zealand National Seismic Hazard Model should revise the northern Hikurangi subduction seismic sources so that rupture does not uplift Puatai Beach and Pakarae River mouth and include new near-shore upper-plate faults as multifault sources.

The consequences of Canadian Cordillera thermal regime in recent tectonics and elevation: a reviewThis article is one of a series of papers published in this Special Issue on the theme Lithoprobe — parameters, processes, and the evolution of a continent.Geological Survey of Canada Contribution 20090195.

2010 ◽  
Vol 47 (5) ◽  
pp. 621-632 ◽  
Author(s):  
R. D. Hyndman
Keyword(s):  
Thermal Regime ◽  
Upper Mantle ◽  
High Surface ◽  
Plate Boundary ◽  
High Elevation ◽  
Mantle Xenoliths ◽  
Tectonic Activity ◽  
Small Scale ◽  
Canadian Cordillera ◽  
Crust And Upper Mantle

The crust and upper mantle thermal regime of the Canadian Cordillera and its tectonic consequences were an important part of the Cordillera Lithoprobe program and related studies. This article provides a review, first of the thermal constraints, and then of consequences in high surface elevation and current tectonics. Cordillera and adjacent craton temperatures are well constrained by geothermal heat flow, mantle tomography velocities, upper mantle xenoliths, and the effective elastic thickness, Te. Cordillera temperatures are very high and laterally uniform, explained by small scale convection beneath a thin lithosphere, 800–900 °C at the Moho, contrasted to 400–500 °C for the craton. The high temperatures provide an explanation for why the Cordillera has high elevation in spite of a generally thin crust, ∼33 km, in contrast to low elevation and thicker crust, 40–45 km, for the craton. The Cordillera is supported ∼1600 m by lithosphere thermal expansion. In the Cordillera only the upper crust has significant strength; Te ∼ 15 km, in contrast to over 60 km for the craton. The Cordillera is tectonically active because the lithosphere is sufficiently weak to be deformed by plate boundary and gravitational forces; the craton is too strong. The Canadian Cordillera results have led to new understandings of processes in backarcs globally. High backarc temperatures and weak lithospheres explain the tectonic activity over long geological times of mobile belts that make up about 20% of continents. They also have led to a new understanding of collision orogenic heat in terms of incorporation of already hot backarcs.

scholarly journals Stratigraphic and tectonic framework of Late Cretaceous and Paleogene strata of southern Aotea Basin, northwest New Zealand

2021 ◽  
Author(s):  
◽  
Callum Skinner
Keyword(s):  
New Zealand ◽  
Late Cretaceous ◽  
System Analysis ◽  
Plate Boundary ◽  
Petroleum Exploration ◽  
Tectonic Activity ◽  
Small Scale ◽  
Southern Boundary ◽  
Seismic Reflection Data ◽  
Reflection Data

<p>Seismic reflection data reveal thick sediment sequences of Late Cretaceous to Paleogene age in the region northwest of Taranaki Basin. A new stratigraphic framework for latest Cretaceous and Paleogene strata is created based on stacking patterns and stratal termination relationships of seismic reflectors. Sequence-bounding reflectors are tied to petroleum exploration wells, including recently-drilled Romney-1, to assign age and paleoenvironment interpretation. I identify the following sequences: (1) a late Haumurian to Teurian (68 – 56 Ma) aggradational shelf sequence, with at least two regressional events linked to eustatic sea-level falls; (2) a diachronous deepening of the basin that progressed from north to south during the late Waipawan to Heretaungan (53 – 46 Ma); (3) small-scale volcanism at the southern boundary with Taranaki Basin is contemporaneous with this deepening; (4) a prograding delta on Challenger Plateau during the Porangan to Runangan (46 – 35 Ma) that is evidence for tectonic uplift of the basin margins; and (5) an onlapping sequence from latest Runangan to present (35 – 0 Ma) that indicates Challenger Plateau subsided 1,300 m. A revised set of paleogeography maps and generalised stratigraphic chart summarise these observations. The Eocene phase (52-46 Ma) of tectonic subsidence and diffuse volcanism is one of the earliest signs of tectonic activity associated with development of the Cenozoic plate boundary through New Zealand. Petroleum system analysis reveals that southern Aotea Basin is prospective for petroleum exploration, with 3 plays identified in the Late Haumurian to Teurian (79 – 56 Ma) strata, in spite of Romney-1 proving unsuccessful.</p>

scholarly journals Hydrogeological Changes along a Fault Zone Caused by Earthquakes in the Moncayo Massif (Iberian Chain, Spain)

2020 ◽  
Vol 12 (21) ◽  
pp. 9034
Author(s):  
Eugenio Sanz ◽  
Ignacio Menéndez Pidal ◽  
José Ignacio Escavy ◽  
Joaquin Sanz de Ojeda
Keyword(s):  
Fault Zone ◽  
Elastic Deformation ◽  
Initial Point ◽  
Historical Earthquakes ◽  
Fracture Site ◽  
Seismic Events ◽  
Confined Aquifer ◽  
Discharge Point ◽  
Moderate Seismicity ◽  
Iberian Chain

The response of springs to earthquakes in the zone of moderate seismicity associated with the fault under study (the Talamantes–Castilruiz fault, Soria, Spain) always leads to a flow decrease regardless of the magnitude of the earthquake and the distance from the epicenter. The sensitivity of the springs is explained by the different degrees of the confinement of their aquifers. The semi-confined aquifer of the Vozmediano spring (1100 L/s) experiences short post-seismic events with a variable decrease in flow and an increase in turbidity, depending on the intensity of the earthquakes felt at the site (Intensity). These changes are likely due to elastic deformation and an increased permeability in their aquifers. This spring is an example of how previous (historical) earthquakes can break the aquifer through the fault causing horizontal movements of the groundwater and displacing the discharge point to a different fracture site located six kilometers from the initial point.

The 2020 volcano-tectonic unrest at Reykjanes Peninsula, Iceland: stress triggering and reactivation of several volcanic systems

2021 ◽  
Author(s):  
Halldór Geirsson ◽  
Michelle Parks ◽  
Kristín Vogfjörd ◽  
Páll Einarsson ◽  
Freysteinn Sigmundsson ◽  
...  
Keyword(s):  
Earthquake Swarm ◽  
Plate Boundary ◽  
Tectonic Activity ◽  
Volcanic System ◽  
Multiple Systems ◽  
The North ◽  
Stress Changes ◽  
Uplift Rates ◽  
Source Models ◽  
Reykjanes Peninsula

&lt;p&gt;The Reykjanes Peninsula in south-west Iceland straddles the North-America - Eurasia plate boundary and hosts several active volcanic systems, including the Svartsengi volcanic system. The last eruption in this area took place around 1240 CE, with eruptive episodes recurring every 800-1000 years, affecting one volcanic system at a time, but spanning multiple systems &amp;#160;with activity spaced ~100 to 200 years. In January 2020, unrest was identified in Svartsengi, characterized by intense seismicity and inflation at a rate of 3-4 mm per day. This area is located within 5 km of several important infrastructures: a) the town of Grindav&amp;#237;k; b) the Svartsengi geothermal power plant; c) and the Blue Lagoon geothermal spa, which had over a million annual visits before the Covid pandemy.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Two continuously recording GNSS stations were installed in the Svartsengi geothermal area in 2013-2015 to monitor geothermally-induced subsidence.&amp;#160; Coinciding with the onset of an earthquake swarm starting on January 21 (M&lt;4), uplift of about 3-4 mm/day was noticed in automated GNSS and InSAR results. The uplift rates in this first inflation phase decreased after January 31 and reverted to slight subsidence in early February. Interestingly, the most intense seismicity was offset from the uplift center by about 2-4 km to the southeast. Geodetic source models from the initial two weeks indicate the deformation is the result of a sill intrusion at a depth of about 4 km &amp;#160;with a volume change of approximately 3 &amp;#160;million m&lt;sup&gt;3&lt;/sup&gt;. The resulting stress changes from this intrusion act to increase seismicity at the sill edges, thus offering an explanation for why the seismicity is offset from the center of uplift. The location of the sill coincides roughly with a crustal volume with a high V&lt;sub&gt;p&lt;/sub&gt;/V&lt;sub&gt;s&lt;/sub&gt; ratio.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Two more inflation-deflation episodes have occurred at Svartsengi in 2020 and the total uplift amounts to approximately 12 cm. Additionally, at least one inflation episode occurred in the Reykjanes system, in February 2020, and inflation started in the Kr&amp;#253;suv&amp;#237;k system in mid-July 2020, culminating in a M5.6 earthquake on October 20. The Fagradalsfjall system, between Kr&amp;#253;suv&amp;#237;k and Svartsengi, has shown high seismicity in 2020, but does not display detectable inflation nor deflation. Therefore, the volcano-tectonic activity in 2020 spans the entire western part of the Reykjanes Peninsula. The stress changes for each of these events are too small to explain the cross-system activity, hence we suggest the entire unrest is &amp;#160;by deep magma migration beneath the entire western Reykjanes Peninsula.&amp;#160;&amp;#160;&lt;/p&gt;

scholarly journals Stratigraphic and tectonic framework of Late Cretaceous and Paleogene strata of southern Aotea Basin, northwest New Zealand

2021 ◽  
Author(s):  
◽  
Callum Skinner
Keyword(s):  
New Zealand ◽  
Late Cretaceous ◽  
System Analysis ◽  
Plate Boundary ◽  
Petroleum Exploration ◽  
Tectonic Activity ◽  
Small Scale ◽  
Southern Boundary ◽  
Seismic Reflection Data ◽  
Reflection Data

<p>Seismic reflection data reveal thick sediment sequences of Late Cretaceous to Paleogene age in the region northwest of Taranaki Basin. A new stratigraphic framework for latest Cretaceous and Paleogene strata is created based on stacking patterns and stratal termination relationships of seismic reflectors. Sequence-bounding reflectors are tied to petroleum exploration wells, including recently-drilled Romney-1, to assign age and paleoenvironment interpretation. I identify the following sequences: (1) a late Haumurian to Teurian (68 – 56 Ma) aggradational shelf sequence, with at least two regressional events linked to eustatic sea-level falls; (2) a diachronous deepening of the basin that progressed from north to south during the late Waipawan to Heretaungan (53 – 46 Ma); (3) small-scale volcanism at the southern boundary with Taranaki Basin is contemporaneous with this deepening; (4) a prograding delta on Challenger Plateau during the Porangan to Runangan (46 – 35 Ma) that is evidence for tectonic uplift of the basin margins; and (5) an onlapping sequence from latest Runangan to present (35 – 0 Ma) that indicates Challenger Plateau subsided 1,300 m. A revised set of paleogeography maps and generalised stratigraphic chart summarise these observations. The Eocene phase (52-46 Ma) of tectonic subsidence and diffuse volcanism is one of the earliest signs of tectonic activity associated with development of the Cenozoic plate boundary through New Zealand. Petroleum system analysis reveals that southern Aotea Basin is prospective for petroleum exploration, with 3 plays identified in the Late Haumurian to Teurian (79 – 56 Ma) strata, in spite of Romney-1 proving unsuccessful.</p>

Uplifted marine terraces of Cephalonia island, Western Greece. Insights into the late Quaternary geomorphic evolution of the area.

2021 ◽  
Author(s):  
Konstantinos Tsanakas ◽  
Giannis Saitis ◽  
Niki Evelpidou ◽  
Efthimios Karymbalis ◽  
Anna Karkani
Keyword(s):  
Sea Level ◽  
Late Quaternary ◽  
Small Region ◽  
Tectonic Activity ◽  
Vertical Movements ◽  
Main Island ◽  
Geomorphic Evolution ◽  
North West ◽  
Marine Terraces ◽  
Western Greece

&lt;p&gt;Uplifted marine terraces act as a continuous record of eustatic changes in tectonically active coastal areas and can provide significant insight into their late Quaternary geomorphic evolution. Cephalonia island, located at the north-west edge of the Hellenic Arc, is a tectonically and seismically highly active area in the Ionian Sea, western Greece, where collision, subduction and transformation take place in a relatively small region. Pleistocene eustatic sea level fluctuations and the long-term vertical movements of the island, have left their imprint on the southern part of the island in the form of uplifted marine terraces. In the present study we aim to identify and map in detail the uplifted marine terraces, applying Digital Elevation Model analysis, utilizing GIS techniques and extensive fieldwork. A GIS spatial geodatabase has been organized and a GIS-based Automatic Landform Analysis was implemented for the identification and mapping of the inner edge of the uplifted marine terraces. Extensive field work and UAV imagery, enabled us to validate the results of the DEM analysis and to improve the accuracy of the position of the inner edges. A sequence of eight marine terraces has been revealed in the Paliki Peninsula ranging in elevation between 2-16 m above sea level for the lowest terrace and 300-440 m asl for the higher one. In the southern part of the main island 9 marine terraces have been identified and mapped at elevations ranging from 1-2 m for the lower one up to 142-170 m above sea level for the higher one respectively. The majority of the terraces is curved on erodible Pliocene and Pleistocene formations and only the lower ones appear to be well preserved. Their lateral morphological continuity is interrupted by the fluvial activity of a large number of ephemeral streams. The non-uniform occurrence of marine terraces at different elevations in Paliki peninsula and the southern part of the main island implies a complex tectonic activity of the island probably attributed to different tectonic blocks.&lt;/p&gt;

Role of the Crustal deformation processes on the seismicity: An approach, using combined dense GNSS velocity field in Europe

2021 ◽  
Author(s):  
Jesus Piña-Valdés ◽  
Anne Socquet ◽  
Céline Beauval ◽  
Pierre-Yves Bard ◽  
Marie-Pierre Doin ◽  
...  
Keyword(s):  
Velocity Field ◽  
Strain Rate ◽  
Vertical Velocity ◽  
Seismic Activity ◽  
Tectonic Activity ◽  
Tectonic Deformation ◽  
Horizontal Deformation ◽  
Continental Scale ◽  
Moderate Seismicity ◽  
The Impact

&lt;p&gt;The impact of the crust deformation on the processes that control the seismic activity is still controversial. The seismic activity is usually thought to be associated with the active tectonic deformation as estimated from the horizontal displacements field: seismic active regions are usually dominated by important horizontal deformation controlled by tectonic activity. But this is not so clear on regions of low to moderate seismicity, where small horizontal deformation rates are commonly observed, similar to the rates detected for regions of no seismicity. In those regions, the non-tectonic processes such as the Glacial Isostatic Adjustment (GIA), may have a significant impact on the seismicity.&lt;/p&gt;&lt;p&gt;Since the deformation of low tectonic activity in Europe is usually piecewise, we combined 10 different GNSS velocity field solution to generate a dense GNSS solution to derive the 3D strain rate at continental scale: using the velocity solutions of common stations, the different datasets were converted to a common reference frame. Their uncertainties were homogenized, and a combined velocity field was computed considering the homogenized uncertainty of each independent solution. Finally, an automatized criterion of identification and outliers removal was applied, as well an adaptive smoothing scheme that depends on the station density, the noise, and the local tectonic deformation rate&lt;/p&gt;&lt;p&gt;The resulting 3D combined GNSS velocity field was interpolated and the horizontal strain rate was derived. Then, assuming the Hooke law for the earth crust, we decompose the vertical velocity field into a component due to tectonic deformation and a component due to isostatic rebound. To better understand the effects of horizontal tectonic deformation versus the flexure generated by GIA on the seismicity, the spatial distribution of the seismicity is compared to the strain rate map and the vertical velocity fields.&lt;/p&gt;

Integrated geophysical data for investigating the tectonic structures in eastern Taiwan

2020 ◽  
Author(s):  
Hao Kuo-Chen ◽  
Zhuo-Kang Guan ◽  
Wei-Fang Sun ◽  
Chun-Rong Chen
Keyword(s):  
Seismic Reflection ◽  
Plate Boundary ◽  
Seismic Array ◽  
Magnetic Survey ◽  
Eurasian Plate ◽  
Tectonic Structures ◽  
Sedimentary Deposits ◽  
Aftershock Sequences ◽  
Short Period ◽  
Dense Seismic Array

&lt;p&gt;The Taiwan orogeny is forming along a complex plate boundary in which the Eurasian Plate (EUP) is subducting eastward beneath the Philippine Sea Plate (PSP). This complex plate boundary is situated in eastern Taiwan and results in large earthquakes occurred frequently in this region. For instance, in 1951, 1972, 1986, 2003, 2006, 2013, 2018, and 2019, earthquakes with magnitude greater than 6 occurred near or along the plate boundary and most of them caused serious damages. However, due to the complexity of the plate boundary from south to north of eastern Taiwan, the seismogenic structures for those events are very different. In order to understand the tectonic structures thoroughly in eastern Taiwan, we planned a integrated geophysical experiment, including seismic reflection, dense seismic array deployments, and magnetic survey from 2016 to 2020. There are 8 seismic reflection profiles along the Longitudinal valley from north to south. As a result, the seismic images show that the sedimentary deposits can reach ~1 km thickness in the northern part and is shallower toward to the southern part. The rocks below the sedimentary deposits are from the east flank of the Longitudinal valley, which belongs to the Eurasian plate. The dense array deployments from 2016-2019 around eastern Taiwan with 1-5 km spacing and totally more than 300 short-period stations deployed. During the deployments, we have captured two aftershock sequences in the north of eastern Taiwan in 2018 and 2019. The seismogenic zones with high-resolution tomography from dense seismic array data sets reveal that the plate interaction between the EUP and PSP. The physical behaviors of the seismogenic zones are related to the collision to subduction along the plate boundary from south to north. Also, the results of the magnetic survey in eastern Taiwan show that the high magnetic anomalies only sparsely distribute, which indicates the volcanic arc may not widely occupy than previous geological investigation. The results of this experiment provide a new thought of the tectonic processes along the plate boundary in eastern Taiwan.&lt;/p&gt;

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