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Teori Plat Tektonik. Teknik Gempa DIII Teknik Sipil Jurusan Pendidikan Teknik Sipil dan Perencanaan FT UNY 2009. Fisiografi : bentuk permukaan planet .
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Teori Plat Tektonik Teknik Gempa DIII Teknik Sipil Jurusan Pendidikan Teknik Sipil dan Perencanaan FT UNY 2009
Fisiografi : bentuk permukaan planet • Divisi dasar permukaan bumi memperlihatkan bahwa permukaan bumi dibagi atas daerah kontinental dan daerah lautan, dimana daerah lautan mengambil sekitar 60% luas daerah permukaan dan 40% diambil oleh kontinental. • Sebuah transect, atau potongan melintang, memotong di sepanjang kontinen hingga ke lautan memperlihatkan sebagian divisi-divisi fisiografi utama.
Fisiografi : bentuk permukaan planet • Gunung-gunung merupakan bagian yang terelevasi naik dari kontinen dan membentuk daerah yang relatif kecil di permukaan bumi di atas permukaan laut. • Kebanyakan daerah luasan kontinental berada di elevasi di bawah 1000 kaki (300 m), dengan gunung yang tertinggi mencapai hampir 30000 kaki (8854 m).
Fisiografi : bentuk permukaan planet • Pada sisi yang berkebalikan dari spektrum, dasar lautan memiliki kedalaman tipikal antara 2,5 – 3 mil (4 – 5 km) dengan transisi yang kasar ke atas hingga ke garis pantai dan transisi ke bawah hingga ke beberapa palung yang sangat dalam dengan kedalaman lebih dari 36000 kaki (11040 m). • Garis pantai merupakan daerah-daerah yang sangat dinamis dimana daratan bertemu dengan lautan dan secara konstan bergeser ke belakang dan ke depan terhadap waktu geologis sebagai sebuah respon terhadap perubahan-perubahan ketinggian air laut.
Tipe-tipe pergerakan lempeng plat tektonik • Divergent Plate Boundary • Convergent Plate Boundary • Transform Plate Boundary
Divergent Plate Boundary • Divergent plate boundaries are axes of spreading where a plate splits and is pulled apart. These boundaries are uplifted by upwelling heat and characterized by tensional stresses that produce block faulting, fractures and open fissures. Basaltic magma derived from partial melting of the mantle is injected into the fissures and extruded to form new seafloor. • The initial rift zone in the disruption of a continent is marked by the introduction of oceanic crust between continental crust blocks and a general uplift. These oceanic-to-continental crust boundaries are passive margins and tectonic activity is minor once separation is achieved.
Divergent Plate Boundary • At the present time, East Africa is bowed upward in a broad arch which is splitting at the crest, forming a linear rift valley marked by volcanic activity and the formation of pillow lava . This is a first step in the passive margin, divergent boundary. As the process continues, the rift floor will sink and oceanic crust will grow. • There is already oceanic crust in the Afar region of the African rift valley. As the margins spread, the flow will cool and subside, forming an oceanic area like the Red Sea. The passive margins are relatively free of mountain chains and tectonic activity since they lie within a plate.
Convergent Plate Boundary • Plate convergence, where plates collide, are tectonically active with complicated geological processes, including igneous activity , crustal deformation, and mountain building (orogeny). The collision and subduction of plates may follow many patterns, but several basic responses can be related to modern tectonic situations. • When oceanic crust meets continental crust, the oceanic plate subducts. As the Nacza plate moves under South America, earthquakes and volcanic activity are associated with the Andes. Subduction destroys oceanic crust and reduces the oceanic area.
Transform Plate Boundary • Transform Plate Boundaries are locations where two plates slide past one another. The fracture zone that forms a transform plate boundary is known as a transform fault. Most transform faults are found in the ocean basin and connect offsets in the mid-ocean ridges. A smaller number connect mid-ocean ridges and subduction zones • Transform faults can be distinguished from the typical strike-slip faults because the sense of movement is in the opposite direction (see illustration above). A strike-slip fault is a simple offset, however, a transform fault is formed between two different plates, each moving away from the spreading center of a divergent plate boundary. When you look at the transform fault diagram above, imagine the double line as a divergent plate boundary and visualize which way the diverging plates would be moving.
