Dynamic Planet

Earthquakes

Primary hazards:
• Ground movement and shaking
• Earthquakes emit body waves, which travel through the earth, and surface waves. S-Waves may cause buildings to collapse and underground pipelines to break.
• Buckling railroad tracks
• Roads cracking and buckling; bridges giving way; shattering of glass and injuries / deaths resulting from these.
Secondary Hazards:
• Soil Liquefaction – Solid material changes to liquid state. Foundations of buildings may be damages
The objects at risk – buildings, roads, facilities.
• Landslides – Often a result of ground shaking. This can overrun building and bury people.
The objects at risk – population, facilities, pipelines, electrical lines, buildings, roads, railways.
• Tsunami (title waves) – 90% occur is the Pacific basin. The more movement and the shallower the focus, the larger the wave.
The objects at risk – ports, port facilities, boats, population, buildings, pipelines.
• Fires - Moderate ground shaking can break gas and electrical lines, sever fuel lines, and overturn stoves. Water pipes rupture, making it impossible to fight the earthquake-caused fires.
• Rockfalls - rough stone materials are located on the slopes. The rockfalls are frequently accompanied by mud flows and landslides
Objects at risk – road and railway traffic, people, communication systems.

• Homelessness may be caused by all of this

General Recommendations for risk reduction
- Mapping the potentially hazardous zones of the expected appearance of the secondary effects.
- Dissemination of the information for the expected secondary effects in case of a strong earthquake among the population.
- Marking the zones of possible secondary effects by different techniques.
Preventive measures
- Strengthening (Upgrade) hazardous zones where and when possible.
Including in the Civil Defense plans the adequate measures for the expected secondary effects.
- Insurance of the facilities against the risks of the secondary earthquake effects.




Plate Boundaries

Continental – Continental: If the oceanic crust is completely subducted the two remaining continental plates will collide to form fold mountains as the sediment on the old sea floor is compressed and uplifted.
This type of boundary has no volcanic activity and earthquakes are mainly shallow focus. E.g. Himalayas, formed by the collision of the Indian plate with the Eurasian plate.

Continental – Oceanic: The denser oceanic plate sinks or is subducted beneath the continental plate in a subduction zone. The continental plate is compressed to form a mountain range and deep ocean trench e.g. Peru-Chile trench and Andes

Oceanic – Oceanic: When oceanic plates collide, a volcanic island arc is produced as the denser plate melts and magma rises to the surface.
E.g. Kurile, Aleutian and Tonga islands

Divergent Plate Boundary - Oceanic: When a divergent boundary occurs beneath oceanic lithosphere, the rising convection current below lifts the lithosphere producing a mid-ocean ridge. Extensional forces stretch the lithosphere and produce a deep fissure. When the fissure opens, pressure is reduced on the super-heated mantle material below. It responds by melting and the new magma flows into the fissure. The magma then solidifies and the process repeats itself.
The Mid-Atlantic Ridge is a classic example of this type of plate boundary. The Ridge is a high area compared to the surrounding seafloor because of the lift from the convection current below. (A frequent misconception is that the Ridge is a build-up of volcanic materials, however, the magma that fills the fissure does not flood extensively over the ocean floor and stack up to form a topographic high. Instead, it fills the fissure and solidifies. When the next eruption occurs, the fissure most likely develops down the center of the cooling magma plug with half of the newly solidified material being attached to the end of each plate.
The Mid-Atlantic Ridge exposed above sea level on the island of Iceland, and 2) the Mid-Atlantic Ridge between North America and Africa.
Effects that are found at a divergent boundary between oceanic plates include: a submarine mountain range such as the Mid-Atlantic Ridge; volcanic activity in the form of fissure eruptions; shallow earthquake activity; creation of new seafloor and a widening ocean basin.


Faults:

Dip-Slip Normal:



Dip-Slip Reverse:


Strike-Slip:
The movement along a strike-slip fault is approximately parallel to the strike of the fault, meaning the rocks move past each other horizontally.

The San Andreas is a strike-slip fault that has displaced rocks hundreds of miles. As a result of horizontal movement along the fault, rocks of vastly different age and composition have been placed side by side. The San Andreas fault is a fault zone rather than a single fault, and movement may occur along any of the many fault surfaces in the zone. The surface effects of the San Andreas fault zone can be observed for over 600 miles (1,000 km).

Normal faults form when the hanging wall drops down. The forces that create normal faults are pulling the sides apart, or extensional.

Reverse faults form when the hanging wall moves up. The forces creating reverse faults are compressional, pushing the sides together.

Together, normal and reverse faults are called dip-slip faults, because the movement on them occurs along the dip direction—either down or up, respectively.

Strike-slip faults have walls that move sideways, not up or down. That is, the slip occurs along the strike, not up or down the dip. In these faults the fault plane is usually vertical, so there is no hanging wall or footwall. The forces creating these faults are lateral or horizontal, carrying the sides past each other.

Strike-slip faults are either right-lateral or left-lateral. That means someone standing near the fault trace and looking across it would see the far side move to the right or to the left, respectively. The one in the picture is left-lateral.

Transform boundary:aka conservative plate boundary and transform boundary

Transform Boundaries
Places where plates slide past each other are called transform boundaries. Since the plates on either side of a transform boundary are merely sliding past each other and not tearing or crunching each other, transform boundaries lack the spectacular features found at convergent and divergent boundaries. Instead, transform boundaries are marked in some places by linear valleys along the boundary where rock has been ground up by the sliding. In other places, transform boundaries are marked by features like stream beds that have been split in half and the two halves have moved in opposite directions.