Tectonic Record of Deformation in Intraplate Domains: Case Study of Far-Field Deformation in the Grands Causses Area, France

Although tectonic plates are usually considered as rigid blocks, intraplate deformation such as lithospheric buckling or diffuse brittle deformation has been recognized for a long time. However, the origin of these deformations remains puzzling. Indeed, whereas the chronology of deformation at plate boundaries can be constrained by numerous methods (syntectonic sedimentary record, thermochronology, etc.), dating of brittle structures (faults, veins, and joints) in the far-field domains remains challenging, preventing a global interpretation of the system as a whole. In this contribution, we have combined a tectonic study with a synkinematical geochronological study of fault-related calcites of the Grands Causses intraplate domain, north of the Pyrenean orogeny. We show that these faults record a much longer history of deformation than previously thought. The Mesozoic extension, usually attributed to an early Jurassic Tethysian rifting event, probably lasted until the Barremian-Aptian epoch, in response to the Pyrenean basin’s opening. The so-called “Pyrenean deformation” of the Grands Causses domain, usually associated with the paroxysm of deformation in the belt during the late Eocene, began much earlier, around 100 Ma, and lasted for more than 60-70 Ma. This study demonstrates the high sensitivity of an intraplate domain (Grands Causses area) to record extensional or compressional deformations occurring at the edge of neighbouring plates.

New ideas about the Balkan peninsula East Part morphotectonics

The article introduces the results of the author’s new investigations about the origin, Quaternary morphotectonic evolution and the modern morphostructure of the Bulgarian Continental Microplate in the eastern part of Balkan Peninsula. The research was realized on a base of the contemporary Plate tectonic study principia by means of the morphostructural analysis apply. It was provided the principal relief building role of the regional mosaic pattern and the listric faulting in the Balkan Peninsula East Part.

Seismisitas di Wilayah Jawa Tengah dan Sekitarnya Berdasarkan Hasil Relokasi Hiposenter dari Empat Jaringan Seismik Menggunakan Model Kecepatan 3-D

ABSTRAK Relokasi hiposenter merupakan suatu metode yang digunakan untuk mendapatkan parameter-parameter gempa yang presisi. Parameter-parameter tersebut digunakan untuk studi tektonik lanjut seperti seismic hazard assessment pada suatu area. Penggunan model kecepatan 3-D secara teori akan memberikan hasil yang lebih baik dibandingkan dengan model 1-D karena model kecepatan di bawah permukaan bumi lebih mendekati model 3-D. Sebanyak 767 event gempa yang direkam oleh jaringan seismik DOMERAPI, MERAMEX, BMKG, dan BPPTKG digunakan pada penelitian ini. Gempa-gempa tersebut direlokasi dengan model kecepatan 3-D dan dianalisis untuk studi seismotektonik di wilayah Jawa Tengah dan sekitarnya. Hasil relokasi hiposenter menggunakan model kecepatan 3-D berhasil mendeteksi sejumlah fitur tektonik secara lebih jelas seperti struktur kolom yang berkaitan dengan Struktur backthrust di selatan Kebumen. Penampang vertikal arah barat-timur yang melewati Sesar Opak mengindikasikan arah dip bidang sesarnya ke arah timur. Zona seismik ganda yang terdeteksi pada studi sebelumnya tidak bisa teridentifikasi dengan baik pada studi ini. Sejumlah gempa volcano-tectonic (VT) berkaitan dengan aktivitas magma dangkal Gunung Merapi terdeteksi juga dengan jelas pada studi ini.ABSTRACT Hypocenter relocation is a method used to get precise earthquake parameters. They will be useful for an advanced tectonic study like seismic hazard assessment in an area. The hypocenter relocation using a 3-D velocity model will theoretically obtain better results than a 1-D velocity model because the earth subsurface model is closed with a 3-D model. Some 767 earthquakes recorded by DOMERAPI, MERAMEX, BMKG, and BPPTKG networks used in this research. They were relocated by using a 3-D velocity model and analyzed for seismotectonic study in Central Java area and its surroundings. The result of hypocenter relocation using a 3-D velocity model is successfully detecting some tectonic features more clearly like columnar structure related to the backthrust structure at the south of Kebumen. The west-east vertical cross-section crossing the Opak fault indicates the dip of the fault plane is directing to the east. This study could not identify the double seismic zone, which was detected by the previous research. Some volcano-tectonic (VT) earthquakes related to the shallow magma activity of Mount Merapi also are detected clearly in this study.

Active Fault Zones of The 2006 Yogyakarta Earthquake Inferred from Tilt Derivative Analysis of Gravity Anomalies

The 2006 Yogyakarta Earthquake had caused a disaster in Bantul area. Several institutions had reported different results for the epicenter location. However, aftershocks studies indicated that the rupture area was at about 10 km east of Opak Fault. Analysis of gravity anomaly, including several degrees of residual anomalies and tilt derivative, facilitated this regional tectonic study to determine the structural constraints on the main earthquake and its aftershocks. The Yogyakarta area was primarily characterized by several SW-NE faults; one of them is the Opak Fault. Among those faults,, there are a series of WNW-ESE faults. Several groups of these lineations indicated a presence of some pairs of parallel strike-slips faults that formed pull-a-part basins. The obtained structural pattern has signified the dynamic response of the force from the subduction of the Australian Plate toward Sunda (Eurasia) Plate. The subduction force produced the strike-slip fault in a parallel direction of subduction, and subsequently, the faults caused the formation of thrust structures that are perpendicular to them.Gempabumi Yogyakarta pada tahun 2006 telah menyebabkan bencana di daerah Bantul dan sekitarnya. Lokasi episenter yang ditentukan oleh beberapa lembaga menunjukkan hasil yang berbeda. Tetapi analisa gempabumi susulan telah menunjukkan daerah pegerakan hingga 10 km ke sebelah timur dari Sesar Opak. Analisa anomali gayaberat yang terdiri dari perhitungan anomali sisa dan turunan kemiringan (tilt derivative) diharapkan dapat membantu studi tektonik regional dalam menentukan batasan struktur yang menyebabkan kejadian gempabumi di daerah Yogyakarta. Daerah ini dicirikan oleh sesar-sesar berarah BD (Barat daya)-TL (Timur laut), yang salah satunya adalah Sesar Opak. Di antara sesar-sesar tersebut, terdapat pula deretan sesar-sesar berarah BBL (Barat barat laut)-TTG (Timur tenggara). Beberapa kelompok kelurusan-kelurusan membentuk kemungkinan adanya cekungan pull-a-part, yang terbentuk karena adanya deretan sesar-sesar strike-slip. Pola struktur yang diperoleh menunjukkan respon dinamik dari subduksi Lempeng Australia terhadap Lempeng Eurasia (Sunda). Tekanan dari gaya subduksi menyebabkan terbentuknya sesar-sesar strike-slip. Kemudian sesar-sesar tersebut menyebabkan adanya struktur sesar naik yang tegak lurus terhadapnya.