1. Geologic Hazards
Geologic Hazards are those Earth processes that are harmful to humans and/or their property.
Includes:
Earthquakes
Volcanic eruptions
Floods
Landslides and other forms of mass wasting

2. Effects of Hazards Primary effects Secondary effects Tertiary effects
Direct result of the event (lava flow, ground motion, etc).
Secondary effects
Associated with, but not a direct response to the event (mudslides, tsunamis, famine and disease, etc).
Tertiary effects
Long term or permanent changes due to the event (change in topography, climate change, habitat loss, etc).

3. Hazard vs Risk
Hazard assessment focuses on characterizing the physical effects of a geologic event.
Risk assessment focuses on the extent of damage (loss) anticipated.
Assessments must provide the information in a form that can be readily used by community planners and decision makers.

4. Hazard Assessment
Determine what the event would be like if it occurred now.
Location and date of past events.
Magnitude and frequency of past events.

5. Risk Assessment
Risk is the probability of a loss within a specific area/time due to a hazardous event.
Risk assessment combines:
Hazard assessment
Location of buildings, facilities, roads, etc.
Exposure to physical effects of event.
Vulnerability - potential for losses.

6. Earthquake Hazards Primary Effects of Earthquakes Ground motion
Faulting and ground rupture

7. Earthquake Hazards Secondary Effects of Earthquakes: Aftershocks
Tsunamis (seismic sea waves)
Landslides
Liquefaction and compaction
Fires/disruption of municipal services

8. Earthquake damage Dependent upon:
Intensity and duration of seismic vibrations
Frequency of seismic activity
Local surface geology
Amplification of seismic waves
Population density/distribution
Local construction practices
Natural resonance
Emergency response/community preparation

9. Natural Resonance Every object has its own natural vibration period.
Hardrock resonance is ~0.5 sec
Sediments resonance is 1-2 sec
Buildings, resonance increases about 0.1 seconds per story, or
0.1 sec for one-story,
0.5 sec for four-story, and
1 to 2 sec for ten to twenty stories.

10. Forecasting Earthquakes
Long-term forecasting
Based on knowledge of tectonic cycles and historical earthquake frequency and intensity.
Paleoseismicity - dating of prior earthquakes
Seismic gaps - locked fault segments
Seismic risk mapping - based on nature and intensity of expected seismic events.

11. Predicting Earthquakes
Short-term prediction
Based on observations of precursor phenomena
Evidence of micro-crack formation
Electrical conductivity
Water levels
Radon and other soil-gas levels
Foreshocks
Animal behavior

12. Earthquakes in Ohio Hazard assessment Tectonic setting
Proximity to New Madrid Seismic Zone
Historical records
Frequency felt since 1776
infrequency of events limits ability to establish frequency
Magnitude - 14 caused moderate damage
Recent events
1980 Sharpsburg Kentucky M = 5.3
1998 western Pennsylvania M = 5.2

13. Earthquakes in Ohio Risk assessment
Location of people, facilities, etc
Preparedness
Exposure
Construction practices
For more information visit the Ohio DNR at: