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GROUND RUPTURES

Calle, Patricia Angelus

Junatas, John Paulo

Roxas, Jean Bailey

What is ground rupture?

Ground Ruptures

Earthquakes occur by the sudden motion along lithospheric breaks called faults. During strong earthquakes, faulting may reach the earth’s surface as ground ruptures.

Ground Ruptures

HOW IT IS FORMED?

An earthquake is generated when a fault moves. When an earthquake is strong enough, faulting initiated at depths may breach the earth’s surface to form a ground rupture. Faulting tends to occur along zones of weakness such as old or pre-existing faults, fractures (or rock breaks not involving slip), or along bedding planes (contacts between sedimentary rock layers and between different types of rocks.

>The Lithosphere breaks when its strength ...

>The Lithosphere breaks when its strength is overcome by the large amount of stress applied.

>Rock failure that involves the slipping of lithosphere blocks past each other is called faulting.

Earthquake-generating faults may propagate to the surface to form ground ruptures. Other faults are called blind if their ruptures do not reach the surface.

Earthquake-generating faults may propagate to the surface ...

ACTIVE FAULTING

As plate positions and stress directions change, younger faults form but many of the older faults are reactivated when the applied stress is large enough to overcome resistance along fault planes. Such faults are called active, as they have been found to have moved under current stress field and have caused earthquakes during historical times and in the recent geological past.

ACTIVE FAULT MAP IN THE PHILIPPINES

Characteristics of Ground Ruptures

LENGTH

The ground rupture length depends on the magnitude of the earthquake. Earthquakes with magnitude 6.5 or greater are generally strong enough to produce large-scale ground ruptures. There is no clear-cut relationship between ground rupture length and earthquake magnitude but larger earthquakes tend to have ranges of longer ground ruptures.

WIDTH

The width of deformation along the length of the ground rupture also largely depend on the type of faulting.

It may form more complex fault patterns.

>The complexity varies along the length of ground. Thus, the zone of deformation may include subsidiary branches and secondary faults on either side of the narrow main break or rupture.

Difference from other deformation features

Difference from other deformation features

Aside from ground rupture, faulting causes movement of the ground in many ways depending on the type of faulting involved. It may cause lateral shifting uplift, subsidence, extension or compression. In addition to variation in size and orientation, different faults can accommodate different styles of rock deformation, such as compression and extension. Not all faults intersect Earth's surface, and most earthquakes do no rupture the surface. When a fault does intersect the surface, objects may be offset or the ground may cracked, or raised, or lowered.

Uplift, in geology, vertical elevation of the Earth's surface in response to natural causes. Broad, relatively slow and gentle uplift is termed warping in contrast to the more concentrated and severe orogeny, the uplift associated with earthquakes and mountain building.

Subsidence is the motion of a surface (usually, the earth's surface) as it shifts downward relative to a datum such as sea level. The opposite of subsidence is uplift, which results in an increase in elevation.

Extension refers to the pulling apart of the Earth's crust and lithosphere.

In geology, the term compression refers to a set of stress directed toward the center of a rock mass, or the squishing of rocks in the lithosphere.

Factors affecting the characteristics of ground ruptures

These factors include the type of fault movement (reverse, normal, or strike-slip) and the inclination of the fault plane.

Strike-slip fault

Strike-slip faults are vertical (or nearly vertical) fractures where the blocks have mostly moved horizontally. If the block opposite an observer looking across the fault moves to the right, the slip style is termed right lateral; if the block moves to the left, the motion is termed left lateral.

The 1990 Luzon earthquake struck the Philippines ...

The 1990 Luzon earthquake struck the Philippines at 4:26 p.m. on July 16 (PDT). 3:26 p.m. (PST) with an estimated moment magnitude of 7.7 and a maximum Mercalli intensity of IX (Violent) and produced a 125 km-long ground rupture that stretched from Dingalan, Aurora to Cuyapo, Nueva Ecija.

Normal fault

Normal fault

Normal faults generally occur in places where the lithosphere is being stretched. Consequently they are the chief structural components of many sedimentary rift basins (e.g. the North Sea) where they have major significance for hydrocarbon exploration. They can also be found in deltas, at the rear edges of huge gravitation slumps and slides.

The 1994 Mindoro earthquake occurred ...

The 1994 Mindoro earthquake occurred at 03:15:30 PST on November 15 near Mindoro, the Philippines. It had a moment magnitude of 7.1 and a maximum Mercalli intensity of VII (Very strong).

Thrust fault

Thrust fault

A thrust fault is a break in the Earth's crust, across which younger rocks are pushed above older rocks.

The 2013 Bohol earthquake occurred on October 15 ...

The 2013 Bohol earthquake occurred on October 15 at 8:12:31 PST in Bohol, an island province located in Central Visayas, Philippines. The magnitude of the earthquake was recorded at Mw 7.2, with epicenter 6 kilometres (3.7 mi) S 24° W of Sagbayan, and its depth of focus was 12 kilometres (7.5 mi).

Can we predict earthquakes?

Scientists have tried lots of different ways of predicti...

Scientists have tried lots of different ways of predicting earthquakes, but none have been successful. They have a pretty good idea of where an earthquake is most likely to hit, but they still can't tell exactly when it will happen.

However, the probability of a future earthquake can be calculated, based on scientific data. Scientists at the US Geological Society (USGS) estimate that the probability of a major earthquake occurring in the San Francisco Bay area over the next 30 years is 67%.

MIKE BLANPIED works for USGS and studi...

MIKE BLANPIED works for USGS and studies earthquake prediction.

>It's good to know if earthquakes are probable, so that residents can prepare. It would be better to predict exactly when earthquakes will occur.

Measures to minimize the effects of ground ruptures

Constructing Seismic Hazard Maps

In many regions, seismic expectancy maps or hazard maps are now available for planning purposes. The anticipated intensity of ground shaking is represented by a number called the peak acceleration or the peak velocity.

To avoid weaknesses found in earlier earthquake hazard maps, the following general principles are usually adopted today:

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1. The map should take into account not only the size but also the frequency of earthquakes.

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2. The broad regionalization pattern should use historical seismicity as a database, including the following factors: major tectonic trends, acceleration attenuation curves, and intensity reports.

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3. Regionalization should be defined by means of contour lines with design parameters referred to ordered numbers on neighboring contour lines (this procedure minimizes sensitivity concerning the exact location of boundary lines between separate zones).

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4. The map should be simple and not attempt to micro zone the region.

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5. The mapped contoured surface should not contain discontinuities, so that the level of hazard progresses gradually and in order across any profile drawn on the map.

Can you think of other ways by which the effects of ground ruptures to man-made structures can be minimized?

Developing resistant structures

Developing resistant structures

Developing engineered structural designs that are able to resist the forces generated by seismic waves can be achieved either by following building codes based on hazard maps or by appropriate methods of analysis. Many countries reserve theoretical structural analyses for the larger, more costly, or critical buildings to be constructed in the most seismically active regions, while simply requiring that ordinary structures conform to local building codes. Economic realities usually determine the goal, not of preventing all damage in all earthquakes but of minimizing damage in moderate, more common earthquakes and ensuring no major collapse at the strongest intensities. An essential part of what goes into engineering decisions on design and into the development and revision of earthquake-resistant design codes is therefore seismological, involving measurement of strong seismic waves, field studies of intensity and damage, and the probability of earthquake occurrence.

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