Early Results of P Wave Regional Tomography Study at Sunda-Banda Arc using BMKG Seismic Network

Abstract The plate movement, geological structure, magmatism, and seismic activity in the area of Bali to East Nusa Tenggara are mainly related with the subducting of Indo-Australian Plate underneath the Eurasian plate. The complexity is added with the recent collision of Australian continent lithosphere with the western Banda arc, along the islands of Flores, Sumba and Timor island. Our study area is known as the Sunda-Banda arc transition. With the aim of imaging subsurface structure, we perform seismic tomography inversion using regional events. We collected 5 years of earthquake data (January 2015 – December 2019) from the Indonesian Agency of Meteorology, Climatology, and Geophysics (BMKG). The output of our data processing is not limited to only P wave velocity model, but also relocated seismicity pattern in the region. In general, seismicity pattern shows dominant shallow events in the south that progressively shift into deeper events in the north down to a few 500 km, marking a dipping subduction zone in this region. A group of shallow events down to a depth of 50 km is also seen at the norther region that may relate to back-arc thrust activity. P wave tomogram model show a lower velocity perturbation at a depth of 30 km that could be associated with magmatic activity along the volcanic front line. Higher P wave perturbation model are spotted at two different zones, the first one is marking a dipping Indo-Australian plate down to depth of 400 km. We noticed that the angle of dipping is steeper in the Eastern part compared to the Western part. The second a relatively flat at shallow depth at the northern region from the island of Lombok to Nusa Tenggara Timur that may mark the back-arc thrust region

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PEMETAAN BAHAYA GEMPA BUMI DAN POTENSI TSU-NAMI DI BALI BERDASARKAN NILAI SEISMISITAS

BULETIN FISIKA ◽

10.24843/bf.2017.v18.i01.p04 ◽

2017 ◽

Vol 18 (1) ◽

pp. 20

Author(s):

Bayu Baskara ◽

I Ketut Sukarasa ◽

Ardhianto Septiadhi

Keyword(s):

Northern Region ◽

Maximum Magnitude ◽

Eurasian Plate ◽

The South ◽

The North ◽

Australian Plate ◽

Back Arc ◽

Sea Area ◽

Earthquake Data

Bali is one of the areas prone to earthquake and tsunami as being at the junction of two plates, namely the Eurasian plate and the Indo-Australian plate is located in the south of Bali and back arc trust zones are located in the North of Bali. We need research on the potential dangers of earthquakes and tsunami in Bali are based on the value of seismicity which is interpreted by the value of b and a. This study uses earthquake data on the coordinates 6?-11? SLand 114?-116? EL with 339 data that was processed using Zmap in order to obtain the value of b at 1.57 ± 0.008 and the value of a is 10.6 and maximum magnitude of 7.1 Mw. From mapping the values ??of b and a known area that has the highest value of b and a lies in the sea area to the south of Bali, Karangasem and Buleleng to the northern region of Bali. Furthermore, for mapping the tsunami in Bali using the TOAST application obtained tsunami prone areas of Bali, Kuta Beach, East Buleleng and Karangasem.

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Subduction dynamics, tectonics, and dynamic topography in the Banda-Java subduction zone

10.5194/egusphere-egu21-9654 ◽

2021 ◽

Author(s):

Laurent Husson ◽

Nicolas Riel ◽

Sonny Aribowo ◽

Christine Authemayou ◽

Danny Hilman Natawidjaja ◽

...

Keyword(s):

Subduction Zone ◽

Mantle Flow ◽

Dynamic Topography ◽

Australian Plate ◽

Banda Arc ◽

Slab Rollback ◽

Australian Continent ◽

Slab Tearing ◽

Back Arc ◽

Dynamic Subsidence

At the far end of the Tethyan realm, the Indo-Australian plate subducts in the Java and Banda trenches. Across the trench, a checkerboard-like distribution of continental and oceanic units sets the geodynamic stage since the Australian continent docked into the subduction zone a few Myr ago: to the East, the Australian continent now subducts and collides with the mostly oceanic Wallacea while to the West, the Indian oceanic plate subducts underneath continental Sundaland. We hypothesize that this fast and transient geodynamic regime explains many observations that characterize the region over the last few Myr: slab rollback and formation of the Banda arc, subsidence of the Weber superdeep seafloor to more than 7000 m, back-arc thrusting in Flores, dynamic subsidence in Sundaland and Sahul, and controversial slab tearing underneath Timor. We set out to model subduction dynamics accounting for the complex assemblage of plates in a real-Earth perspective, using the fast thermo-mechanical code LaMEM that allows dealing with complex setups. Our results predict the winding of the subduction zone around Papua, ultimately retreating into the Banda embayment, thereby causing the extreme dynamic subsidence of the Banda seafloor. Geometrical consistency imposes coeval slab tearing underneath Timor while the slab rolls back. The formation of the Flores backthrust quickly follows Australian collision with Wallacea and propagates westward in continental Sundaland. Shortening rates quickly drop tenfold while entering Sundaland, in Java, in agreement with kinematic and structural observations. In the geologically near future, the back-arc thrust is predicted to reverse the subduction polarity, Wallacea being on the brink to subduct southward underneath Australia. Last, transient mantle flow expectedly causes dynamic subsidence in Sahul and Sundaland, thereby profoundly remodeling the physiography of the entire region.

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The Australian Plate and underlying mantle from waveform tomography with massive datasets

10.5194/egusphere-egu21-5272 ◽

2021 ◽

Author(s):

Janneke de Laat ◽

Sergei Lebedev ◽

Bruna Chagas de Melo ◽

Nicolas Celli ◽

Raffaele Bonadio

Keyword(s):

Structural Information ◽

Azimuthal Anisotropy ◽

P Wave ◽

Depth Range ◽

S Wave ◽

Crust And Upper Mantle ◽

Southern Boundary ◽

Velocity Anomaly ◽

Australian Plate ◽

Australian Continent

We present a new S-wave velocity tomographic model of the Australian Plate, Aus21.&#160; It is constrained by waveforms of 0.9 million seismograms with both the corresponding sources and stations located within the half-hemisphere centred at the Australian continent. Waveform inversion extracts structural information from surface, S- and multiple S-waves on the seismograms in the form of a set of linear equations. These equations are then combined in a large linear system and inverted jointly to obtain a tomographic model of S- and P-wave speeds and S-wave azimuthal anisotropy of the crust and upper mantle. The model has been validated by resolution tests and, for particular locations in Australia with notable differences with previous models, by independent inter-station measurements of surface-wave phase velocities, which we performed using available array data.&#160;&#160;Aus21 offers new insights into the structure and evolution of the Australian Plate and its boundaries. The Australian cratonic lithosphere occupies nearly all of the western and central Australia but shows substantial lateral heterogeneity. It extends up to the northern edge of the plate, where it is colliding with island arcs, without subducting. The rugged eastern boundary of the cratonic lithosphere provides a lithospheric definition of the Tasman Line. The thin, warm lithosphere below the eastern part of the continent, east of the Tasman Line, underlies the Cenozoic volcanism locations in the area. The lithosphere is also thin and warm below much of the Tasman Sea, underlying the Lord Howe hotspot and the submerged part of western Zealandia. A low velocity anomaly that may indicate the single source of the Lord Howe and Tasmanid hotspots is observed in the transition zone offshore the Australian continent, possibly also sourcing the East Australia hotspot. Another potential hotspot source is identified below the Kermadec Trench, causing an apparent slab gap in the overlying slab and possibly related to the Samoa Hotspot to the north. Below a portion of the South East Indian Ridge (the southern boundary of the Australian Plate) a pronounced high velocity anomaly is present in the 200-400 km depth range just east of the Australian-Antarctic Discordance (AAD), probably linked to the evolution of this chaotic ridge system.

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GEOCHEMICAL VARIATIONS ON HOSTED VOLCANIC ROCKS OF CIBALIUNG EPITHERMAL GOLD MINERALISATION, BANTEN – INDONESIA: IMPLICATIONS FOR DISTRIBUTION OF SUBDUCTION COMPONENTS

Journal of Applied Geology ◽

10.22146/jag.7216 ◽

2015 ◽

Vol 6 (1) ◽

Author(s):

Anastasia Dewi Titisari ◽

David Phillips ◽

Hartono Hartono

Keyword(s):

Trace Element ◽

Volcanic Rocks ◽

Epithermal Gold ◽

Eurasian Plate ◽

Magmatic Arc ◽

Incompatible Elements ◽

Australian Plate ◽

Banda Arc ◽

Geochemical Variations ◽

Subduction Component

Subduction of the Indo-Australian Plate beneath the Eurasian Plate formed at least seven magmatic arcs in Indonesia. One of the magmatic arcs is the Neogene Sunda-Banda arc hosts various style of gold mineralisation such as Cibaliung epithermal gold mineralisation. Major and trace element data for host volcanic rocks to the Cibaliung epithermal gold mineralisation is provided by this study to identify the magmatic arc system and the distribution of subduction components. Enriched LILE (Large Ion Lithopile Element) and LREE (Light Rare Earth Element) compositions for basaltic andesite – rhyodacitic samples from the Cibaliung district are characteristic of calc-alkaline arcs. In this typical volcanic arc, the subduction component can be shown to make a dominant contribution to its content of LILE such as Rb, K, Th, and Ba enriched (more than 88%) relative to the mantle and within plate inputs. The incompatible elements (Hf, Zr, and Nb) cannot be observed in the subduction component and thus assumed to be derived from trace element enriched sub-continental lithosphere. These incompatible elements are defined as conservative elements therefore it suggests that the magma occurrence is related to a hydrous slab component. Keywords: Subduction, Indo-Australian plate, magmatic arcs, volcanic rocks, Cibaliung, epithermal gold.

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Complex structure of the lithospheric slab beneath the Banda arc, eastern Indonesia depicted by a seismic tomographic model

Research in Geophysics ◽

10.4081/rg.2011.e1 ◽

2011 ◽

Vol 1 (1) ◽

pp. 1 ◽

Cited By ~ 4

Author(s):

Sri Widiyantoro ◽

Jeremy D. Pesicek ◽

Clifford H. Thurber

Keyword(s):

Upper Mantle ◽

Velocity Structure ◽

Complex Structure ◽

P Wave ◽

Zone Structure ◽

Study Region ◽

Tomographic Images ◽

P Wave Velocity ◽

Banda Arc ◽

Back Arc

Seismic tomography with a non-linear approach has been successfully applied to image the P-wave velocity structure beneath the Banda arc in detail. Nearly one million compressional phases including the surfacereflected depth phases pP and pwP from events within the Indonesian region have been used. The depth phases have been incorporated in order to improve the sampling of the uppermantle structure, particularly below the Banda Sea in the back-arc regions. For the model parameterization, we have combined a highresolution regional inversion with a low-resolution global inversion to allow detailed images of slab structures within the study region and to minimize the mapping of distant aspherical mantle structure into the volume under study. In this paper, we focus our discussion on the upper mantle and transition zone structure beneath the curved Banda arc. The tomographic images confirm previous observations of the twisting of the slab in the upper mantle, forming a spoon-shaped structure beneath the Banda arc. A slab lying flat on the 660 km discontinuity beneath the Banda Sea is also well imaged. Further interpretations of the resulting tomograms and seismicity data support the scenario of the Banda arc subduction rollback.

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Initial Result of P Wave Tomography Model in Sunda-Banda Arc Transition using FMTOMO

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/873/1/012057 ◽

2021 ◽

Vol 873 (1) ◽

pp. 012057

Author(s):

P T Brilianti ◽

Haolia ◽

M I Sulaiman ◽

S S Angkasa ◽

S Widyanti ◽

...

Keyword(s):

Velocity Structure ◽

Tectonic Setting ◽

Shallow Depth ◽

P Wave ◽

Benioff Zone ◽

Target Area ◽

Fast Marching Method ◽

Eurasian Plate ◽

Fast Marching ◽

Banda Arc

Abstract Our study area is located near island Sumbawa, Sumba, Flores, West Timor, Indonesia and East Timor, popularly known as Sunda-Banda arc transition zone. The tectonic setting is mainly controlled by the movement of the oceanic lithosphere Indo-Australian plate subducting the Eurasian plate and Northward migration of Australian continental lithosphere into western Banda-arc in the region of Flores, Sumba and Timor island. We tried to image velocity structure beneath these regions using regional events and tomography inversion model. We collected 5 years of regional events from the Indonesian Agency of Meteorology, Climatology and Geophysics. In total, we reserved 3186 events recorded on 29 stations. For data processing, we used fast marching method as ray tracing between sources and receiver. We then employed subspace inversion as the tomography procedure to estimate the best velocity model representing the tectonic model in the region. Hypocenter data distribution is concentrated on shallow parts of the region and along the Benioff zone down to a maximum depth of 400 km. One of challenge of this study is that although events are abundance, the stations used are mostly located onshore and does not extend in the south-north direction that leads us to under determined problem in the inversion process. However, checker-board models show most our target area can be retrieved to its initial model with sign of smearing effects shown start from a depth of 50 km. After six iteration and optimized selection of damping and smoothing parameters, we observed low velocity anomaly under Bali, Lombok, Sumba, East Nusa Tenggara at shallow depth that may be related with volcanic activity. Deeper low anomaly can also be seen that may be related with partial melting process. A band of fast velocity is clearly seen that goes deepen to the north depicting subducting slabs own to a depth of 300 km. We also observed a possible of fast velocity in the northern part of our stations at shallow depth that we believe may represent the back arc thrust.

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Early Results of Eastern Indonesia P-wave Tomography Study Using Regional Events

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/873/1/012068 ◽

2021 ◽

Vol 873 (1) ◽

pp. 012068

Author(s):

M I Sulaiman ◽

P A Subakti ◽

Haolia ◽

D Y Fatimah ◽

I Madrinovella ◽

...

Keyword(s):

P Wave ◽

S Wave ◽

Low Velocity ◽

Seismicity Pattern ◽

Velocity Anomaly ◽

Eastern Indonesia ◽

The North ◽

Early Results ◽

Slab Tear ◽

Tectonic System

Abstract The tectonic system of Eastern Indonesia is controlled by several major and minor plates, such as Indo-Australian, Australian plate, and Pacific plates. This area is known for its complexity, and high seismic activity. This study tries to image the complex structures beneath this region by employing regional events data and seismic tomography methods. We used five years of regional events catalog provided by the Indonesian Agency of Meteorology, Climatology, and Geophysics. We have sorted 7336 events recorded between 120° – 136° longitude and 0° – 13°(-) latitude consisting of 46446 P and 15467 S wave arrival data. Relocated hypocenter map shows a better constrain location on seismicity along outer Bandar Arc. A dipping pattern of seismicity is seen that is going deeper to the Banda Sea. The seismicity map also images a steep angle pattern of seismicity that could be related to the subduction slab roll-back model at North of Wetar island. Interestingly, we spotted a seismicity gap in West Seram that could be linked with slab tear zone. The checker-board test suggests a proper resolution is still reliable to a depth of 200 km with a less interpretable model at a depth of 300 km. P-wave tomographic models image the high velocity dipping down going slab. The Banda slab is seen to subduct from south Timor Island to the north, from east Tanimbar and Aru Island to west part, and from north Seram Island to south. We observed the down-going slab meet from all directions at about 300 km beneath the Banda sea. P wave tomogram also shows the Timor Island slab has a steeper dip that agrees with the seismicity pattern. Near the Seram island, we identify a low-velocity anomaly zone infiltrate the Banda slab beneath the shallow part of West Seram, which was previously interpreted as slab tear zone. This study also noticed a higher velocity tomogram model at North of Wetar island that might indicate a back-arc thrust. Lastly, a low-velocity band is also exposed at a shallow depth close to the volcano chain along that Banda volcanic arc.

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EDUKASI DAN MITIGASI GEMPA PADA BANGUNAN

Prosiding SENAPENMAS ◽

10.24912/psenapenmas.v0i0.15017 ◽

2021 ◽

pp. 417

Author(s):

Daniel Christianto ◽

Sunarjo Leman ◽

Alvira Nathania Tanika ◽

Maria Kevinia Sutanto ◽

Vryscilia Marcella

Keyword(s):

General Information ◽

Physical Contact ◽

Eurasian Plate ◽

Earthquake Mitigation ◽

Natural Event ◽

Australian Plate ◽

The Pacific ◽

Prone Area ◽

Tectonic Earthquakes ◽

The Impact

A natural disaster is a natural event that has a major impact on the human population. One of the natural events that became the focus of this PKM activity was an earthquake. Earthquakes are natural events in the form of vibrations or wavy movements on the earth's crust caused by internal forces. Earthquakes caused by shifting of the ground are called tectonic earthquakes and earthquakes caused by volcanoes are called volcanic earthquakes. Indonesia is an earthquake-prone area because it is located on three plates, namely the Eurasian Plate, the Pacific Plate, and the Indo-Australian Plate. Only in western, central and southern Kalimantan, the source of the earthquake was not found. To reduce the impact of risk during an earthquake, it is necessary to carry out an earthquake mitigation to the community in areas prone to earthquakes. Earthquake mitigation that will be carried out in this PKM activity is in the form of counseling through online webinars to prevent physical contact or crowds, related to the Covid19 pandemic. As a result, from the questions asked by participants, there is still a lack of understanding of the dangers of changing the function of the building or the building's use limit based on the design load and the condition of the building after the earthquake. So for the next PKM, it is recommended to make general information guidelines such as examples of photos or pictures about the condition of buildings that need to be reviewed for repairs or are no longer suitable for use after being hit by an earthquake.Bencana alam adalah suatu peristiwa alam yang mengakibatkan dampak besar bagi populasi manusia. Salah satu peristiwa alam yang menjadi fokus dalam kegiatan PKM ini adalah gempa bumi. Gempa bumi merupakan fenomena alam berupa getaran atau gerakan bergelombang pada lempeng bumi yang disebabkan oleh tenaga yang berasaldari dalam bumi. Gempa yang disebabkan oleh pergeseran tanah dinamakan gempa tektonik dan gempa yang disebabkan oleh gunung berapi dinamakan gempa vulkanik. Indonesia merupakan daerah rawan gempa karena terletak di atas tiga lempeng yakni Lempeng Eurasia, Lempeng Pasifik, dan Lempeng Indo-Australia. Hanya di Kalimantan bagian barat, tengah, dan selatan, sumber gempa bumi tidak ditemukan. Untuk mengurangi dampak resiko pada saat gempa perlu dilakukan suatu mitigasi gempa kepada masyarakat di daerah yang rawan terjadi gempa bumi. Mitigasi gempa yang akan dilakukan dalam kegiatan PKM ini berupa penyuluhan melalui webinar secara online untuk mencegah kontak fisik atau kerumunan, berhubungan dengan pandemi Covid19. Hasilnya, dari pertanyaan yang diajukan peserta, masih kurang pemahaman bahaya dari mengubah fungsi guna bangunan atau batas guna bangunan berdasarkan beban desain dan kondisi bangunan setelah gempa. Maka untuk PKM selanjutnya, disarankan membuat panduan informasi secara umum seperti contoh foto atau gambar tentang kondisi bangunan yang perlu ditinjau untuk perbaikan atau tidak layak guna lagi setelah terkena gempa.

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Lithospheric architecture of the Ligurian Basin from seismic travel time tomography

10.5194/egusphere-egu21-2822 ◽

2021 ◽

Author(s):

Anke Dannowski ◽

Heidrun Kopp ◽

Ingo Grevemeyer ◽

Grazia Caielli ◽

Roberto de Franco ◽

...

Keyword(s):

Seismic Data ◽

Velocity Model ◽

P Wave ◽

Central Basin ◽

Uppermost Mantle ◽

Mantle Boundary ◽

Oceanic Spreading ◽

Refraction Seismic ◽

Back Arc ◽

Ligurian Basin

The Ligurian Basin is located north-west of Corsica at the transition from the western Alpine orogen to the Apennine system. The Back-arc basin was generated by the southeast retreat of the Apennines-Calabrian subduction zone. The opening took place from late Oligocene to Miocene. While the extension led to extreme continental thinning little is known about the style of back-arc rifting. Today, seismicity indicates the closure of this back-arc basin. In the basin, earthquake clusters occur in the lower crust and uppermost mantle and are related to re-activated, inverted, normal faults created during rifting.To shed light on the present day crustal and lithospheric architecture of the Ligurian Basin, active seismic data have been recorded on short period ocean bottom seismometers in the framework of SPP2017 4D-MB, the German component of AlpArray. An amphibious refraction seismic profile was shot across the Ligurian Basin in an E-W direction from the Gulf of Lion to Corsica. The profile comprises 35 OBS and three land stations at Corsica to give a complete image of the continental thinning including the necking zone.The majority of the refraction seismic data show mantle phases with offsets up to 70 km. The arrivals of seismic phases were picked and used to generate a 2-D P-wave velocity model. The results show a crust-mantle boundary in the central basin at ~12 km depth below sea surface. The P-wave velocities in the crust reach 6.6 km/s at the base. The uppermost mantle shows velocities >7.8 km/s. The crust-mantle boundary becomes shallower from ~18 km to ~12 km depth within 30 km from Corsica towards the basin centre. The velocity model does not reveal an axial valley as expected for oceanic spreading. Further, it is difficult to interpret the seismic data whether the continental lithosphere was thinned until the mantle was exposed to the seafloor. However, an extremely thinned continental crust indicates a long lasting rifting process that possibly did not initiate oceanic spreading before the opening of the Ligurian Basin stopped. The distribution of earthquakes and their fault plane solutions, projected along our seismic velocity model, is in-line with the counter-clockwise opening of the Ligurian Basin.

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Dynamics of the extension in the Fonualei Rift in the northern Lau Basin at 16 °S

10.5194/egusphere-egu21-7605 ◽

2021 ◽

Author(s):

Anna Jegen ◽

Anke Dannowski ◽

Heidrun Kopp ◽

Udo Barckhausen ◽

Ingo Heyde ◽

...

Keyword(s):

Velocity Gradient ◽

Lower Crust ◽

Pacific Plate ◽

P Wave ◽

Upper Crust ◽

Lau Basin ◽

Australian Plate ◽

The Pacific ◽

Refraction Seismic ◽

Roll Back

The Lau Basin is a young back-arc basin steadily forming at the Indo-Australian-Pacific plate boundary, where the Pacific plate is subducting underneath the Australian plate along the Tonga-Kermadec island arc. Roughly 25 Ma ago, roll-back of the Kermadec-Tonga subduction zone commenced, which lead to break up of the overriding plate and thus the formation of the western Lau Ridge and the eastern Tonga Ridge separated by the emerging Lau Basin.As an analogue to the asymmetric roll back of the Pacific plate, the divergence rates decline southwards hence dictating an asymmetric, V-shaped basin opening. Further, the decentralisation of the extensional motion over 11 distinct spreading centres and zones of active rifting has led to the formation of a composite crust formed of a microplate mosaic. A simplified three plate model of the Lau Basin comprises the Tonga plate, the Australian plate and the Niuafo'ou microplate. The northeastern boundary of the Niuafo'ou microplate is given by two overlapping spreading centres (OLSC), the southern tip of the eastern axis of the Mangatolu Triple Junction (MTJ-S) and the northern tip of the Fonualei Rift spreading centre (FRSC) on the eastern side. Slow to ultraslow divergence rates were identified along the FRSC (8-32 mm/a) and slow divergence at the MTJ (27-32 mm/a), both decreasing southwards. However, the manner of divergence has not yet been identified. Additional regional geophysical data are necessary to overcome this gap of knowledge.Research vessel RV Sonne (cruise SO267) set out to conduct seismic refraction and wide-angle reflection data along a 185 km long transect crossing the Lau Basin at ~16 &#176;S from the Tonga arc in the east, the overlapping spreading centres, FRSC1 and MTJ-S2, and extending as far as a volcanic ridge in the west. The refraction seismic profile consisted of 30 ocean bottom seismometers. Additionally, 2D MCS reflection seismic data as well as magnetic and gravimetric data were acquired.The results of our P-wave traveltime tomography show a crust that varies between 4.5-6 km in thickness. Underneath the OLSC the upper crust is 2-2.5 km thick and the lower crust 2-2.5 km thick. The velocity gradients of the upper and lower crust differ significantly from tomographic models of magmatically dominated oceanic ridges. Compared to such magmatically dominated ridges, our final P-wave velocity model displays a decreased velocity gradient in the upper crust and an increased velocity gradient in the lower crust more comparable to tectonically dominated rifts with a sparse magmatic budget.The dominance of crustal stretching in the regional rifting process leads to a tectonical stretching, thus thinning of the crust under the OLSC and therefore increasing the lower crust&#8217;s velocity gradient. Due to the limited magmatic budget of the area, neither the magnetic anomaly nor the gravity data indicate a magmatically dominated spreading centre. We conclude that extension in the Lau Basin at the OLSC at 16 &#176;S is dominated by extensional processes with little magmatism, which is supported by the distribution of seismic events concentrated at the northern tip of the FRSC.

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