formulation of a risk probability rating system for geohazard …119.92.161.2/portal/portals/21/eia...

Formulation of a Risk Probability Rating System for Geohazard and Environmental Risk Assessment

Katherine A. Hipol-Gavile Associate - Environment/ Geologist, AECOM, Taguig City Email: [email protected] The environmental impact assessment process has seen considerable

improvement over the years with respect to identification and characterization of

geohazard in parallel with local developments in the geosciences. However, one

aspect which is lacking is the determination of the frequency and likelihood of

occurrence for the identified geohazards for the purposes of impact and

environmental risk assessments. There is no officially established geohazard

frequency and probability rating in the Philippines comparable to international

rating systems such as those of the Federal Emergency Management Agency

(FEMA) and the United States Geological Survey (USGS). Due to this,

discussions of geohazard frequency and probability within the EIS are often

subjective and undervalued. Current developments in the country’s EIA system

and related regulatory requirements as well as integration of climate change

adaptation and disaster risk reduction schemes in the EIS call for the

establishment and adaptation of a similar rating system. The formulation and

adaptation of a geohazard risk probability rating system is vital in aiding

proponents, preparers and policy makers to 1) Formulate geohazard assessment

that is site specific; 2) Formulate applicable control measures considering the

likelihood of occurrence of the geohazard pre-mitigation; 3) Prioritize specific

geohazards in engineering design and controls; 4) Develop applicable hazard

scenarios to quantify asset loss in case of occurrence; 5) Promote interagency

(DENR-EMB, MGB, PHIVOLCS, and PAGASA) cooperation in formulating a

local hazard rating scheme; and 6) Communicate frequency and probability

assessment to stakeholders and policy makers to enable engagement and

participation in emergency response and disaster preparedness.

About the author

Katherine has about 10 years of experience in the

field of geology and environmental assessment that

include collaboration with foreign groups such as the

U.S Geological Survey. Currently, she works as the

lead for the geology, geohazard, and soils module in

environmental impact assessment and feasibility

studies for AECOM.

Formulation of a Risk Probability Rating System for Geohazard and Environmental Risk Assessment

Katherine A Hipol-Gavile Associate - Environment/ Geologist, AECOM, Taguig City Email: [email protected]

Introduction Due to the Philippines’ geographic location and tectonic setting, projects are generally

prone to different categories and varying degrees of geologic hazards. Moreover, it is

common that multiple geohazards are identified for a project site. Aside from sudden-

onset geohazards (i.e. earthquakes), evident climate change effects have brought about

emergence of geohazards that intensify over time (e.g. mass movement, erosion, and

flooding). While the Philippine Environmental Impact Statement (EIS) process requires

the comprehensive discussion of the geologic hazards and their corresponding impacts

and control measures, the discussions generally concentrate on the identification and

definition of the geohazards, with the assessment of the likelihood of occurrence and

the effects of climate change, undervalued. This paper presents methods and practices

that may improve geohazard impacts assessment in relation to the EIS and the

Environmental Risk Assessment (ERA) as well as the adaptation of a risk probability

rating scheme that may enable assessors and regulators to describe the potential

frequency and likelihood of the occurrence of geohazards for a particular site.

Geohazard Assessment in the Philippine EIA system Geohazards include all hazards that are entirely or partially caused by processes that

occur at the surface or the subsurface of the earth (Aurelio, 2004). Geohazards include

both instantaneous processes (i.e. earthquakes, volcanic eruptions) and chronic events

that develop over time and are often associated with climate change (Wood, 2008).

Recent years have seen the inclusion of hazards brought about by non-geologic

processes but are intensified by climate change (e.g. flooding). To summarize, the

geohazards discussions in the EIS consist of the following categories:

Geohazard Categories Specific hazards

1. Seismicity-related Ground shaking

Ground rupture

Liquefaction

Earthquake-related slope failure

Tsunami

2. Mass movement re

elated and rainfall-related)

Slope failu

(Earthquake-r

Subsidence

Differential Settlement

Creep

3. Volcanism-related earthquakes Volcanic

Lava flows

Pyroclastic flows

Lahar

Ash fall

Eruption-related tsunami

4. Others Erosion

Flooding

Storm surge

Seiches

Often, for a given project site, multip zards may occur that can sometimes

compound or enhance the baseline conditions’ natural susceptibility to particular

ologic events. Added challenges may also be encountered when a proposed project

le geologic ha

ge

changes the existing geomorphology and hydrologic conditions of an area creating

essentially a non-equilibrium or unstable condition. Most of the discussions for this

paper will focus on seismic hazard assessment as an example of an instantaneous

event, and mass movement that may include both instantaneous and non-

instantaneous events as impacted by climate change.

Seismic hazard Assessment The purpose of seismic hazard assessment is to determine the potential risks posed to

tive faults adjacent to or within the project site. Seismic

azard assessment also includes predictive determination of the response of the

identified sources; and

rical summation of contributions of all earthquake

rce.

tic and probabilistic

eismic hazard assessment for a project site. Earthquake frequencies for each source

Mass Movement Hazards Assessment

a project by the presence of ac

h

subsurface to an earthquake, the severity of which is largely dependent on subsurface

foundation properties and occurrence of zones of weaknesses. The seismic hazard

assessment approach consists of the following:

• Identifying seismic sources;

• Determining earthquake frequency from each source;

• Defining ground acceleration values from

• If possible, conducting nume

magnitudes at all distances from the site from each sou

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) certification of

active faults remains a fundamental tool in conducting determinis

s

are determined from historical earthquake databases. In the absence of specific ground

acceleration equations in the Philippines, the equation developed by Fukushima and

Tanaka (1990) is used to define the ground acceleration values from identified sources.

Derived peak ground acceleration (PGA) values for a project site are then correlated

with the 475-year return period of probabilistic seismic hazard assessments from

Thenhaus and others (1996), U.S Geological Survey (2009) and the National Structural

Code of the Philippines (2001). These tools enable preparers to assess not only the

potential impacts of a seismic event to a project site, but also the likelihood of the

occurrence of an event within the project life.

The assessment of mass movement hazards, particularly slope failure, makes use of

e geohazard mapping outputs of the Mines and Geosciences Bureau (MGB) coupled

IS) tools and field surveys. Defining critical

lopes are usually conducted to determine areas susceptible to failure. However, the

he propensity for specific geohazards of a site can be determined through geologic

geology coupled with valuable tools such as GIS and geoscientific data.

he timing of geohazards however, cannot be accurately forecasted, and often,

probability rating was adopted. Risk probability rating descriptors were incorporated as

th

with Geographic Information System (G

s

importance of ground truthing to augment GIS tools and secondary information are

usually neglected. Field information is essential in identifying surface features that

indicate stress and potential failure, enabling the geohazard assessment and the

consequent recommendation of control measures to be more site specific. Identification

of previous occurrence of mass movement (e.g. landslide scarps, tension cracks, and

debris deposits) is valuable in determining not only the susceptibility of an area to failure

but also the type and likelihood by which these events may occur. The risk probability

descriptors for slope failure can thus be formulated from the proposed percentage range

or value vis-à-vis, for example, the impact area.

Risk Probability Rating System for Geohazards: A case study on past mining projects. T

mapping, identification of geomorphologic structures, and understanding of the

subsurface

T

approach to these events is reactionary. It should be noted that people also make

decisions based on forecasts and probabilities (e.g. probability of rain, fatality rates).

Though the occurrence of geohazards cannot be accurately predicted, risk probability

ratings for each geohazard category can be formulated to aid in drafting applicable

mitigating measures and prioritizing the implementation of specific engineering design

and controls based on the likelihood of occurrence.

The Tampakan Cu-Au Mine Project EIS is an example in which a preliminary risk

part of a geohazard assessment matrix to determine the likelihood of occurrence of a

pre-mitigation geohazard within the project site and the risks that it may pose during the

roject life.

, as well as the integration of climate change adaptation (CCA) and

isaster risk reduction (DRR) schemes in the EIS, will call for the establishment and

a probability risk rating system. The formulation and adaptation of a

eohazard rating system for the Philippines is vital in aiding proponents, preparers and

p

Conclusion Eventually, current developments in the country’s EIA system and related regulatory

requirements

d

adaptation of

g

policy makers to 1) Formulate geohazard assessment that is site specific; 2) Formulate

applicable control measures considering the likelihood of occurrence of the geohazard

prior to mitigation; 3) Prioritize specific geohazards in engineering design and controls;

4) Develop applicable hazard scenarios to quantify asset loss in case of occurrence; 5)

Promote interagency cooperation in formulating a local hazard rating scheme; and 6)

Communicate frequency and probability assessment to stakeholders and policy makers

to enable engagement and participation in emergency response and disaster

preparedness. It is important to emphasize that these efforts should be at an

interagency level between those whose main thrust are the geosciences anddisaster

preparedness, and business and government groups who will monitor, mitigate,

respond to or reduce the exposure of vulnerable systems such as the stakeholders and

their assets.

References

urelio, M.A. (2004). Engineering Geological and Geohazard Assessment (EGGA)

system for sustainable infrastructure development: the Philippine experience.

Engineering Geology for Sustainable Development in Mountainous Areas, Free

din (eds) Geological Society of Hong Kong, 7pp.

CH Australia (2009). Australian Master OHS and Environment Guide (2nd ed.).

http://w

A

and Ay

C

Federal Emergency Management Agency Earthquake Hazard Maps

ww.fema.gov/earthquake/earthquake-hazard-maps

.H. and Milner, K.R. (2007). Forecasting California’s Earthquakes –What can we

expect in the next 30 years. U.S Geological Survey Fact

Field, E

Sheet, Stauffer, P.H and

tion for Horizontal

in Japan. Bulletin of the

Hillson

EA Proceedings, 7 pp.

ard in the Philippines. National

Wood, ce to Natural Hazards. U.S

Hendley J.W (eds) 2 pp.

Fukushima, Y., and Tanaka, T. (1990), A New Attenuation Equa

Acceleration of Strong Earthquake Ground Motion

Seismological Society of America, 80, 757-783.

, D.A. (2005). Describing probability: The limitations of natural language. PMI

Global Congress 2005 EM

Thenhaus, P.C., Hanson, S.L., Algermissen, S.T., Bautista, B., C., Bautista, M.L.P.,

Punongbayan, B., Rasdas, A. R., Nillos, J. and Punongbayan, R.S. (1994).

Estimates of the Regional Ground Motion Haz

Disaster Mitigation in the Philippines, DOST-PHIVOLCS, 1994.

N. (2011). Understanding Risk and Resilien

Geological Survey Fact Sheet, Stauffer, P.H and Hendley J.W (eds) 2 pp.

Formulation of a Risk Rating System for Geohazard and Environmental Risk Assessment

Katherine H. GavileAssociate, Environment

June 20, 2013

Hazards are defined as:

Events or physical conditions that have the potential to cause fatalities, injuries, property damage, infrastructure damage, agricultural loss, damage to the environment, interruption of business, or other types of harm or loss (FEMA, 1997)

FEMA. 1997. Multi Hazard Identification and Assessment. FEMA. Washington, D.C.

While Geologic Hazards or Geohazards:

“Include all hazards that are entirely or partially caused by processes that occur at the surface or the subsurface of the earth (Aurelio, 2004).

The Philippines’ tectonic and geographic setting makes most of the country susceptible to different geohazards.

As the population grows, more projects, developments, settlements and people are situated in areas that are prone to geohazards.

The Environmental Impact Assessment (EIA) process requires the comprehensive discussion of the geologic hazards and the corresponding impacts and control measures along with the integration of Climate Change Adaptation and Disaster Risk Reduction.

Geologic Hazard Assessment within the Philippine EIA System

Environmental Impact Statement

Key Baseline Information

The LandThe WaterThe AirThe People

Environmental Risk Assessment

Environmentally Critical Areas

Geology, Geomorphology, and Geohazards

The focus of discussion is mostly on identification of the geologic hazards and thorough assessment is often undervalued.

Geologic Hazard Categories


1. Seismicity-related

Ground shaking

Ground rupture

Liquefaction

Tsunami

2. Mass movement

Slope failure

Subsidence

Differential Settlement

Creep

Geologic Hazard Categories


3. Volcanism-related

Volcanic earthquakes

Lava flows

Pyroclastic flows

Lahar

Ash fall

Eruption-related tsunami

4. Others

Erosion

Flooding

Storm surge

Seismic Hazards

Inquirer.net

August 2, 1968 – Mw 7.3 at Casiguran, Aurora

August 16, 1976 – Mw 8.0 at Moro Gulf

July 16, 1990 – Mw 7.8; 25 km-long ground rupture that stretched from Aurora to Nueva Ecija

August 31, 2012 – Mw 7.6 at Samar

Seismic Hazard Assessment

The purpose of seismic hazard assessment is to determine the potential risks posed to a project by the presence of active faults adjacent to or within the project site.

Seismic hazard assessment also includes predictive determination of the response of the subsurface to an earthquake, the severity of which is largely dependent on subsurface foundation properties and occurrence of weaknesses.


The seismic hazard assessment approach consists of the following:

Identifying seismic sources;

Determining earthquake frequency from each source;

Defining ground acceleration values from identified sources; and

If possible, conducting numerical summation of contributions of all earthquake magnitudes at all distances from the site from each source.


The PHIVOLCS certification of active faults remains a fundamental tool in conducting deterministic and probabilistic seismic hazard assessment for a project site.

The PHIVOLCS certification of active faults is fundamental in identifying potential earthquake generators and determining the instance of seismic sources to a project site.


In the absence of specific ground acceleration equations in the Philippines, the equation developed by Fukushima and Tanaka (1990) is used to define the ground acceleration values from identified sources.

* Based on Fukushima and Tanaka - Bulletin of Seismological Society of America, August 1990


Parameters

Eastern Section Central Section Western Section

9.91 km west of

unnamed Fault

19 km south-west of Fault A

9.85 km south of unnamed

Fault

38.02 km north-east

of Mindanao Fault-

11.65 km south-east

of unnamed Fault

25.71 km south-west of Fault A

Radius (km) 9.900 19.000 9.800 38.000 11.600 25.700

Magnitude (M) 7.500 7.500 7.500 7.500 7.500 7.500

Acceleration (cm/sec2) 457.709 358.328 458.498 231.537 435.703 304.200

Rock (60% of g)* 0.280 0.219 0.280 0.142 0.266 0.186

Hard Soil (107% of g)* 0.499 0.391 0.500 0.253 0.475 0.332

Medium Soil (87% of g)* 0.406 0.318 0.407 0.205 0.386 0.270

Soft Soil (139% of g)* 0.649 0.508 0.650 0.328 0.617 0.431

Table 3.1-16 Calculated G-values for Defined Faults and Seismic Responses per Subsurface Material* Based on Fukushima and Tanaka - Bulletin of Seismological Society of America, August 1990


Derived PGAs for a project site are then correlated with the 475-year return period of probabilistic seismic hazard assessments from Thenhaus et.al. (1996), U.S Geological Survey (2009) and the National Structural Code of the Philippines (2001).


Coupled with probabilistic seismic hazard analysis, it is also important to note the historical earthquake occurrence or distribution for a given site to assess the active earthquake generators and the probability that an earthquake of a certain magnitude will occur.

United States Geological Survey (USGS) NorthernCalifornia Earthquake Data Center (NCEDC) AdvancedNational Seismic System (ANSS) online global earthquakecatalog database.


From Yuen et.al. (2000)


While the identification of seismic hazards associated with potential activities of the nearest active faults or earthquake generators is vital. Assessment should go beyond mere identification for it to be more site and project specific.

The Working Group on California Earthquake Probabilities (WGCEP) recommends estimating seismic hazard probabilities or composite forecasts based on seismology, geology, geodesy, and paleoseismology(Field and Milner, 2007).

Mass Movement

August 2, 1999

November 2004 Blogs.agu.org

Earthdata.nasa.gov

February 17, 2006

Assessment for Mass Movement Hazards

• Geology

• Slope shape and geomorphology

• Concentration of surface water

• Presence and depth to groundwater

• Material strength


USDA recommends the delineation of 18% slopes as critical.

However, for the Philippines, slope failure susceptibility is determined not only by slope gradient but an interplay of factors such as climate, geology, vegetation, soil type, and surface hydrology.

Tools that can be used include GIS, secondary data, and most importantly, ground truthing.

Impact Assessment Criteria and Rating Scales

Criteria Rating ScalesStatus • Positive

• Negative• Neutral

Extent (spatial limit of the impact)

• Local (site-specific or immediate surrounding area)• Regional (Province)• National (Country)

Duration(predicted lifetime of the impact)

• Short-term (0 – 5years)• Medium Term (6 – 15 years)• Long Term (16 years and beyond and where it is assumed the impact will cease after the operational life of the project)

Impact Assessment Criteria and Rating Scales (cont.)

Criteria Rating ScalesIntensity (severity of the impact) • Low (minimal)

• Medium (environment is alteredbut processes continue in a modified manner)• High (permanent or long-term substantial change)

Probability (Likelihood of occurrence)

• Improbable or Rare• Probable – equivalent to Unlikely, < 50% chance or possibility to occur within or after the project life• Highly Probable - equivalent to Possible, 50 to 90% chance or will occur within project life• Definite – equivalent to Likely, >90% chance of occurring or will occur regardless of mitigation measure

Probability Risk Rating System

The timing of geohazards, cannot be accurately forecasted and often, approach to these events is reactionary.

Note that people also make decisions based on forecasts and probabilities (e.g. probability of rain, fatality rates).

Though the occurrence of geohazards cannot be accurately predicted, risk probability ratings for each geohazard category can be formulated to aid in drafting applicable mitigating measures and prioritizing the implementation of specific engineering design and controls based on the likelihood of occurrence.

Probability

• Classical: Probability of getting 2 heads in 3 flips of a coin

• Subjective: Probability of the Philippines becoming no.16 in economy by 2050

• Frequency: Probability of an Ondoy-like rainfall over a 120 year period

Jardine and Hrudley, 1997. “Mixed Messages in Risk Communication”

PROBABILITY DESCRIPTION

ALMOST CERTAIN 1 in 10 chance LIKELY TO OCCUR

LIKELY 1 in 100 chance WILL PROBABLY OCCUR

POSSIBLE 1 in 1000 chance MAY OCCUR OCCASIONALLY

UNLIKELY 1 in 10,000 chance DO NOT EXPECT TO HAPPEN

RARE 1 in 100,000 chance DO NOT BELIEVE WILL EVER HAPPEN

Australia / New Zealand Model (AS/NZS 4360: 1999)

Criteria Rating ScalesProbability(Likelihood of occurrence)

• Improbable – equivalent to FEMA rating of Rare

• Probable – equivalent to Unlikely, < 50% chance or possibility to occur within or after the project life

• Highly Probable - equivalent to Possible, 50 to 90% chance or will occur within project life

• Definite – equivalent to Likely, >90% chance of occurring or will occur regardless of mitigation measure

Thank You

[email protected]

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