Teknik Gempa 03 - Blog at UNY dot AC dot ID

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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
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 perubahanperubahan ketinggian air laut.
Fisiografi : bentuk permukaan planet
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.
Convergent Plate Boundary
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.
Transform Plate Boundary
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