CE442 Geotechnical Earthquake Engineering

Introduction to Geotechnical Earthquake Engineering

• Earthquake Engineering aims to understand and mitigate the impacts of earthquakes on people and their environment.
• It is an interdisciplinary field that combines geology, seismology, geotechnical engineering, structural engineering, risk analysis, and other technical fields.

Historical Perspective

• Earthquake records date back 3000 years in China, nearly 1600 years in Japan and Eastern Mediterranean, and about 350 years in the United States.
• Hundreds of millions of people worldwide live with significant earthquake risk, posing an economic threat to local, regional, and national economies.
• Earthquakes cannot be prevented, but the goal is to mitigate the effects of strong shaking to reduce loss of life, injuries, and damage.

Principal Types of Earthquake Damage

• Structural damage refers to the harm inflicted on buildings, bridges, roads, and other infrastructure due to earthquake forces.
• Seismic hazard includes ground shakings, which can cause damage to structures depending on construction quality, materials, and design.

Seismic Hazard

• Ground shakings can cause damage to structures, and the damage can vary greatly depending on the construction quality, materials, and design.
• Period (T) is the time it takes for one wave cycle to pass a given point, and Frequency (F) is the number of waves that pass through a point in one second.
• Frequency = 1 Hz (cycle per second), and the natural period of a building is the number of seconds it takes for the building to naturally vibrate back and forth.
• If the period of ground motion matches the natural resonance of a building, it will undergo the largest oscillations possible and suffer the greatest damage.
• Soft sediment (soil deposits) can cause high amplitude, low frequency ground shakings, while hard bedrock can cause low amplitude, high frequency ground shakings.
• Attenuation and amplification of seismic waves can occur due to soil conditions, reducing or increasing the energy of seismic waves at certain frequencies.

Destructive Earthquakes in the Philippines

• List of destructive earthquakes in the Philippines, including Ragay Gulf Earthquake (1973), Casiguran Earthquake (1968), and others.

Geotechnical Earthquake Engineering

• Geotechnical earthquake engineering deals with the design and construction of projects to resist earthquake effects.
• It requires an understanding of geology, seismology, and earthquake engineering.
• Geotechnical engineers may need to investigate liquefaction, calculate settlement, check foundation design, and evaluate slope stability and lateral deformation.

Plate Boundaries

• Three types of plate boundaries: transform, convergent, and divergent.
• Transform boundaries are regions where two tectonic plates slide past each other horizontally, causing earthquakes.
• Convergent plate boundaries are regions where two tectonic plates are moving towards each other, leading to subduction, mountain formation, earthquakes, and volcanic activity.

Interiors of the Earth

• The earth is composed of a sequence of shells or layers called geospheres, with the heaviest forming the core.
• The lithosphere (crust) is the thinnest outer solid shell, with a density of 1500 kg/m3 and a temperature of about 25°C.
• The asthenosphere (mantle) is 2685 km thick, surrounding the core, with a density of 5000-6000 kg/m3.
• The outer core is a molten layer of iron and nickel beneath the mantle, extending from 2,900 km to 5,150 km depth.
• The inner core is a solid, dense region at the center of the earth, extending from 5,150 km to the core at 6,371 km depth.

Faults

• Faults are created primarily through tectonic forces and the movement of Earth's lithospheric plates.
• Faults are fractures in the Earth's crust where movement has occurred, resulting in displacement of the rock on either side.
• The point of generation of an earthquake is known as the focus, center, or hypocenter.
• List of active faults in the Philippines, including East Zambales Fault, Iba Fault, and others.

Fundamental Fault Mechanics

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