Earthquakes Flashcards
What is compression?
Pushes on rocks from opposite directions which causes rocks to be shortened parallel to the stress applied
What is tension?
Pulls rocks from opposite directions, resulting it to become stretched/lengthened
What is shear?
Occurs when rocks are being pushed in an uneven manner, causing the rocks to be skewed such that different sides of a rock body slide or move in opposite directions
Rocks near the surface of the earth are __________.
elastic
What is elastic limit?
The point in which they no longer behave elastically and deformation becomes permanent
TRUE or FALSE. When a force that is acting on the elastic rock is removed, the rocks will not return to their original shape
FALSE. it will return to its original shape.
When rocks deform they often slide past one another along a fracture plane, at which point the fracture is called a ______.
FAULT
TRUE or FALSE. All faults then involve some type of slippage or movement, whereas fractures do not
TRUE
What type of fault is the North Bohol Fault?
Reverse Fault with minor right and left lateral displacement
Where and when does Digdig fault rupture? And what is the surface wave magnitude
- Dingalan Aurora to Kayapa Nueva Vizcaya
- July 16, 1990
- 7.8
He is a Scottish geologist who authored the T he Dynamics of Faulting and Dyke Formation with Application to Britain
(Edinburgh, 1942, 1951) and systematized our knowledge of the geometry and stress fields of various faults. He contended that the direction of the maximum principal stress along normal faults is ___________.
Ernest Masson Anderson; vertical
What is sigma 1, 2, and 3 means?
maximum, intermediate, and minimum stress
TRUE or FALSE. In theory, all faults have no rotational component because displacement even in a dip-slip fault varies along the fault length.
FALSE. Have a rotational component
What is seismic waves?
refer to vibrational waves that travel through solid earth
What is Body waves?
travel trough the earth’s interior, spreading outward from the hypocenter in all directions (like sound in air).
What are the two types of Body wave?
Primary and Secondary Waves
What is primary waves?
- Compressional waves
- Parallel to direction the wave is travelling, causing rocks to alternately compress and decompress as successive waves pass through
What is secondary waves?
- transverse/perpendicular to direction of wave
propagation
What is surface wave?
- travel on the earth’s surface away from the epicenter
(like ripples on water) - slowest wave (typically at a speed that is 10% slower than S waves)
- can cause more property damage compared to body waves.
What is rayleigh waves?
- ground roll (similar to rolling waves of ocean)
- move vertically and horizontally
What is love waves?
- Move the ground from side to side in a horizontal plane
Difference between P-wave and S-wave
P-wave
- speed is 4 to 7 km/sec
- first wave to arrive at a station
- can pass through solid and liquid
S-wave
-slow, 2-5km/sec
-arrives at a later time than P-wave does
-can pass through solid but not liquid
The instrument used to detect seismic waves A heavy suspended mass is held as motionless as possible, suspended by springs or hanging it as a pendulum.
Seismometer
A seismometer with a recording device that produces a permanent record of earth motion, usually in the form of wiggly line drawn on a moving strip of paper.
Seismograph
The paper record of earth vibration. The different waves travel at different rates, so they arrive at seismograph stations in a definite order: first P waves, then S waves, and finally, the surface waves.
Seismogram
How to locate earthquakes?
- The interval of arrival between S and P waves is used to calculate the distance of the seismograph station from the earthquake source.
- A single station can record only the distance, not the direction to a quake The location of an earthquake is determined by drawing circles on a map (or globe) with the seismograph stations distributed in different parts of the globe.
Range of shallow depth of focus.
0-70 km
Range of intermediate depth of focus.
70 - 350 km
Range of deep depth of focus.
350 - 670 km
How do earthquakes occur?
- when rocks are subjected to a force, also called stress, they can become deformed or strained.
- When brittle materials reach their elastic limit they undergo permanent deformation by fracturing
- ductile materials deform by flowing plastically.
Two types of earthquake.
Volcanic and tectonic
This theory holds that earthquakes originate when a force (stress) acts on a rock body, causing it to deform and accumulate strain. Eventually, the rock reaches its elastic limit, at which point it ruptures or fails suddenly, releasing the strain it had accumulated
Elastic Rebound Theory
What is epicenter?
Located above the hypocenter/focus
What is hypocenter/focus?
The point where it generally release energy
TRUE or FALSE. Earthquakes occur deeper than 435 miles (700 km) below the surface because the higher temperatures cause the rocks to become so brittle.
FALSE. Do not occur deeper than 435 miles (700 km); plastic flow
Redistribution of strain commonly produces a series of smaller earthquakes.
Aftershocks
Primary earthquake sometimes refer to _________.
Main shock
TRUE or FALSE. Rocks are much stronger under a compressional force compared to a tensional force.
TRUE
TRUE or FALSE. Convergent boundaries where compressive forces dominate, rocks are able to accumulate less strain before rupturing than at divergent boundaries where tensional forces are dominant .
FALSE. more strain
What is fault creep?
The ability of a rock body to store strain is the frictional resistance of the faults.
Based mainly on the knowledge of when and where earthquakes occurred in the past.
Long-term Forecasting
What are the two aspect of long-term forecasting?
Paleoseismology and seismic gap
The study of prehistoric earthquakes. Involves the study of offsets in sedimentary layers near fault zones to determine recurrence intervals of major earthquakes prior to historical records.
Paleoseismology
A zone along a tectonically active area where no earthquakes have occurred recently, but it is known that elastic strain is building in the rocks.
Seismic gap
Involves monitoring of processes that occur in the vicinity of earthquake prone faults for activity that signify a coming earthquake.
Short-term prediction
Anomalous events or processes that may precede an earthquake
Precursor events
Different types of Earthquake precursors
Increase in foreshocks
Slight swelling/uplift or tilting of the ground surface
Decreased electrical resistance
Fluctuating water levels in wells
Increased concentration of radon gas in groundwater
Generation of radio signals
Reduce the actual amount of shear force that can
develop on the structure.
Seismic engineering
Different types of seismic engineering.
Cross bracing and shear walls
Base isolation
Wrapping of columns with a steel jacket
Spiral wrapping technique on vertical reinforcing rods
What type of seismic engineering technique used for outdated buildings?
External skeleton and base isolation
Examples of Non conventional/Non intrusive methods
Microtremor Survey Method
Refraction Microtremor Survey
Horizontal to Vertical Spectral Ratio Method
What type of fault is San Andreas Fault?
a right lateral (dextral) transform fault that separates the Pacific and North American Plates
The network of interlocking faults located on either side.
Fault zone
TRUE or FALSE. In northern California where the San Andreas fault moves offshore the boundary of the North American plate changes from a transform (shear) setting to one of convergence (compression)
TRUE
TRUE or FALSE. Subduction zone earthquakes are capable of releasing unusually large amounts of energy is partly due to the way the overriding plate buckles and becomes locked
The surface area over which the slippage or rupture occurs can be quite large compared to that in other plate settings
The descending oceanic plate is relatively cool, which makes the rocks more brittle and capable of accumulating more strain before rupturing
Some of this energy can be transferred to the ocean, creating tsunamis that reach heights of 100 feet 30 m)
TRUE
Cascadian last major earthquake?
1700 or 300 years ago
Earthquakes that occur far from a plate boundary or active mountain belt and are generally believed to be related to tectonic forces that are being transmitted through the rigid plates
Intraplate earthquake
Example of intraplate earthquake
New Madrid and Charleston seismic zones because they have a history of producing powerful intraplate earthquakes In 1886 a strong earthquake occurred about 50 miles 80 km) outside of Charleston, South Carolina, causing 60 deaths and extensive property
What happened in 1976 Tangshan disaster?
- Intraplate earthquake (Mm. 7.5)
- people have no memory of large earthquake
- the 250,000 to 650,000 people perished
Walls are usually constructed of brick or stone bound together with mortar, as opposed to reinforced walls with internal supports of wood or steel.
unreinforced masonry
Once a floor becomes free, it naturally falls onto the one below, which can cause additional floors to fail in a cascading manner
pancaking
Factors that affect Ground Shaking
Period, Natural Vibration Frequency, and Resonance
Focal Depth and Wave Attenuation
Ground Amplification
The time (in seconds ) it takes for a building to naturally vibrate back and forth
period
TRUE or FALSE. Smaller structure take longer time to vibrate back and forth than larger structures.
FALSE. Shorter
TRUE or FALSE. Period of ground motion is generally controlled by the ground’s stiffness
TRUE
Refers to the vibration of a structure/building at a fixed frequency; frequency is the number of times the motion is repeated in a set amount of time
Natural vibration frequency
TRUE or FALSE. As building height increases, the natural
vibration frequency decreases.
TRUE
When a building’s natural vibration frequency matches the frequency of seismic waves, _________ can occur, causing a building to sway more violently
resonance
Energy of the resulting seismic waves steadily decreases as they travel away from the focus, a process referred to as _________.
wave attenuation
TRUE or FALSE. Seismic waves experience different amounts of wave attenuation , depending on the types of geologic materials the waves pass through.
TRUE
TRUE or FALSE. 1. Loose materials and rocks of lower density will absorb less energy from passing seismic waves compared to rocks that are more rigid and dense
FALSE. more energy
TRUE or FALSE. 2. On areas of rigid rocks, seismic waves are able to retain less of their energy as they travel farther.
FALSE. more of their energy
When seismic waves travel through weaker materials, they slow down and lose energy at a faster rate.
Ground amplification
Secondary earthquake hazards
Liquefaction, Ground displacement, ground fissure, earthquake-induced mass wasting, fires, and tsunami
Who made the intensity scale?
Italian seismologist Giuseppe Mercalli in 1902
A seismic scale used and developed by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) to measure the intensity of an earthquake. It was developed as a response to the 1990 Luzon Earthquake
Philippine Earthquake Intensity Scale (PEIS)
A seismic scale used and developed by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) to measure the intensity of an earthquake. It was developed as a response to the 1990 Luzon Earthquake
Philippine Earthquake Intensity Scale (PEIS)
Before PEIS what type of intensity scale did we use?
Rossi Forel Intensity Scale
Quantify the amount of ground motion during an earthquake, and the energy that was released when the rocks ruptured.
Magnitude Scales
Rates earthquakes based on the size of their seismic waves, as measured by seismographs; governed by amplitude (wave height) and distance
Richter Magnitude Scale (named after the seismologist, Charles F. Richter)
Based on similar types of seismogram measurements as Richter’s, but is more accurate over a wide range of magnitudes and geologic conditions; based on the total
amount of energy released and is determined by measuring the surface area of the ruptured fault
and how far the land moved along the fault.
Moment Magnitude Scale
TRUE or FALSE. 10 fold increase in ground motion this corresponds to about a 30 fold increase in energy released at the focus
TRUE
Classes of magnitude
Great 8.0 or more
Major 7.0 - 7.9
Strong 6.0 - 6.9
Moderate 5.0 - 5.9
Light 4.0 - 4.9
Minor 2.0 - 3.9
Microearthquake 1.0 -1.9
Moro Gulf Earthquake
M w 8.1
Depth: 59 km
Epicenter: 06.3 N, 124.0 E
August 17, 1976 at 12:11 AM
Intensity V in Davao City
Death toll reached up to
3,502 and 1,502 missing
Magnitude 6.7 Surigao del Norte Earthquake
Magnitude 6.7
February 10, 2017
