probabilistic seismic ground motion hazard analysis: a

Seminar on Earthquake Engineering and Disaster Risk Management22 August 2019, Romblon State University

Probabilistic Seismic Ground Motion Hazard Analysis: A Tool for Disaster Risk Management

Henremagne C. PEÑARUBIA

Philippine Institute of Volcanology and Seismology (PHIVOLCS)Department of Science and Technology (DOST), Philippines

OBJECTIVE:

To enhance the engineers’ and disaster managers’

understanding of the potential ground motion hazard

in the region for consideration in the seismic design,

risk assessment and disaster risk management.


Why Engineers should

be concerned?

Deaths caused by

collapsing structures?


• A fault is a break, fracture, fissure or zone of weakness where

movement or displacement had occurred or may occur again. It may

extend hundreds of kilometers across the earth’s surface and tens of

kilometers downward.

• An active fault is a fault that has moved within the last 10,000 years. It

shows evidence or has documented history of its movement.

• A trench is the deepest portion on the sea floor. It is a manifestation of a

subduction zone where a tectonic plate moved or is pushed under by

another tectonic plate.


• Earthquake is a weak to violent shaking of the ground produced by the sudden

movement of rock materials below the earth’s surface. It usually occurs along

tectonic plate boundaries and active faults.

• Ground shaking could be felt in the

vertical and horizontal direction

coupled with circulatory and

oscillatory motion.

• Magnitude may be between 1<Mw >9.5

• Hypocenter varies from 1<depth>800km

http://www.iris.edu


Seismic Hazards observed

in the Philippines

Earthquake HazardsSeminar on Earthquake Engineering and Disaster Risk Management22 August 2019, Romblon State University

PHIVOLCS websitehttps://www.phivolcs.dost.gov.ph


Ground Rupture Hazard Maps - Regional


Provincial Hazard Maps


Fault Finderhttp://www.faultfinder.phivolcs.dost.gov.ph


Liquefaction Hazard Map


• An earthquake can also cause soil materials on a slope to become unstable by the imposed inertial load causing loss of strength in the slope. These landslides and rock falls may be observed on hillsides and mountainous regions experiencing ground shaking intensity greater than PEIS V.


Earthquake-induced Landslide Hazard Map

Tsunami Hazard Map


Earthquake Information Page


Ground Shaking Hazard

• The shaking of the ground caused by the faulting and propagation of released energy

in the form of perceptibly mild to intense vibration at the passage of the seismic waves on

site. The wave train is essentially composed of body waves and surface waves.

• 1. Body waves are either the compressional (push or up) or extensional motion (pull or

down), also called primary wave, or the shear motion (sway or side to side), also called

secondary wave, usually felt as intense shaking but of short duration.

• 2. Surface waves, on the other hand are oscillatory motions orthogonal to the secondary

wave and circulatory motions opposite to the direction of the primary wave. These are

usually less intense felt undulations but relatively of longer duration.


The characteristic of earthquake ground motion which have the greatest impact to houses and structures are:1. duration2. amplitude (displacement, velocity and acceleration)3. frequency of the ground motion


Deterministic Hazard Maps and Tool


•On the right-hand side of PHIVOLCS’ frontpage

are the links to the recently-launched atlases onprobabilistic seismic hazard Analysis (PSHA).

•The PSHA of the Philippines and Metro Manila, also known as the Philippine Earthquake Model

(PEM) Atlasprovides: peak ground acceleration (PGA) maps

on rock site at 10%, 5% and 2% PoE in 50 years.

It also provides:

spectral acceleration (SA) maps at 0.2 sec, 0.5 sec, 0.8 sec, 1.0 sec and

3.0 sec natural periods at 10% PoE in 50 years on stiff soil for the

whole archipelago.


Probabilistic Hazard Maps


National Structural Code of the Philippines (NSCP 2015)

Source: NSCP 2015

F = ma V = 2.5CaIW/R

The more intense the acceleration (g) is,

the larger the force acting on the structure!

Base shear

Figure 208-3, Design Response Spectra

Risk = hazard * exposure * vulnerabilty

avoidance proper construction

Risk Management

reductionminimize control measures

Recommendations• Enhance the engineers, community planners and disaster

managers’ understanding of earthquake hazards, exposure,

and vulnerability of structures and communities.

• Update and strictly implement the seismic design

requirement of the National Structural Code of the

Philippines.

• Invest in building resilient structures and communities.


Your knowledge and course of action may save lives, resources and livelihood!

http://www.phivolcs.dost.gov.ph

http://www.faultfinder.phivolcs.dost.gov.ph

http://gisweb.phivolcs.dost.gov.ph

https://hazardhunter.georisk.gov.ph


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