EQ L4: Forecasting

Question 1

Why forecasting and not “predicting”?

Answer 1

Prediction is too general, implies precision of the future. Forecasting is more short-term, accurate for that time length.

Question 2

Do we know even the most well studied fault? (btw what is the fault called?)

Answer 2

No, there are also hidden faults in this system. Very complex! Most well studied is the San Andreas fault in California.

Question 3

What’s a recent observation to provide more accuracy to the question of forecast location of earthquakes?

Answer 3

Seeing the pattern of stress changes as result of an earthquake. But stresses must be constantly monitored/observed. Expensive! Otherwise, using satellite-based radar measurements, can observe very small changes in ground’s shape. Still in experimental stage.

Question 4

Why is it important to have an idea of how the ground will move should an earthquake occur?

Answer 4

We can build structures to perfectly withstand that motion, and then there will be no more worries about living in earthquake prone regions.

Question 5

In Canada, the Geological Survey of Canada (GSC) has a whole department devoted to…

Answer 5

Seismic Hazard

Question 6

The probability of strong shaking (strong enough to cause significant damage in a fraction of these buildings) is more than 30 times greater in the regions of highest hazard (red areas compared to cream areas). This means that there is at least a __ per cent chance of significant damage within towns of these regions every 50 years than in the regions of lowest hazard (less than 1 per cent chance in 50 years)

Answer 6

30

Question 7

Smaller/Larger buildings are at risk from higher frequency ground motion.

Answer 7

Smaller

Question 8

Taller buildings resonate at lower/higher frequencies than smaller buildings.

Answer 8

Lower

Question 9

On the Parkfield experiment, when did the predicted quake happen?

Answer 9

Sept 2004, ten years “late”

Question 10

What earthquake was successfully ‘predicted’? What then happened to another earthquake? What about Japan?

Answer 10

1975 Haicheng, China. But not the 1976 Tangshan, China. 250 000 deaths.

Japan: early 1990’s prediction efforts, but Kobe earthquake in 1995 catastrophe

Question 11

Generally it is more useful to consider the ____ rather than predicting.

Answer 11

likelihood/ probability

Question 12

Why is the conventional forecast an outdated simplistic, not sensible approach?

Answer 12

Because the Earth is dynamic and constantly changing.

Question 13

What is the Renewal Forecast?

Answer 13

More useful than conventional forecast. If stress increases gradually, then the chance of a shock also grows as time passes.

Question 14

Renewal forecast with consideration of effect of earthquakes nearby. Why considered?

Answer 14

Because earthquake will cause stresses to change. If we’re in the danger zone of an area near a recent earthquake, the likelihood of an earthquake in our area might spike up soon after a nearby earthquake. If we don’t experience one, then probability might decay because of relaxation in the ground.

Question 15

It is better to make informed decisions knowing there are uncertainties, than …

Answer 15

making decisions in total ignorance.

Question 16

Possible indicators of imminent earthquakes?

Answer 16

lights in the sky

changing electrical resistivity in ground, air, ionosphere

spontaneous radio noise

changing height of the ionosphere

changes in infrared light visible from satellites

Question 17

Possible explanation for the observed phenomena preceding earthquakes?

Answer 17

changes in tectonically active regions cause charges to build up and propagate. Varying currents cause electromagnetic signals such as radio signals. They are observable on the ground and/or from low orbit space-based platforms.

Question 18

Other possible predictive observations before earthquake?

Answer 18

ground behaviour (uplift, tilt, creep, ground water levels)

seismicity (patterns of small quakes and motions)

radon emission

animal behaviour

Question 19

Currently, _____ may be more cost-effective than prediction.

Answer 19

prevention

Question 20

What evidence of mega-quake on Jan 26 1700 at 9:00PM do we have?

Answer 20

Tree rings: land appears to have dropped suddenly to slightly below sea level, killing all trees in area. Tree rings indicate event occurred in winter of 1699-1700.

Evidence of changing sediment deposition along the coast. Indicates periodic uplift and sinking. Occurred at the same time as the tree ring events. Series of similar events going back in time in intervals varying between 300 and 900 years.

Records in Japanese coastal communities of a tsunami occurring at around this time. Computer modeling used to establish exactly when the earthquake occurred if its location could be assumed.

Question 21

Investigations at the GSC describe in detail the real-time motion of the western edge of the North American Plate. The monitoring devices record positions relative to a reference location at _____, BC.

Answer 21

Princeton

Question 22

Data gathered from the Victoria area recording plate motion shows interesting features of the Cascadia subduction zone. One of the remarkable observations?

Answer 22

This portion of the western edge of the North American plate has long term motion that is not steady. It is mainly steady at speeds of about 10 mm per year in an eastward direction, but with sudden westward jumps (“silent slip” events) roughly every year. These jumps coincide exactly with periods of increased seismic activity. This activity involves unusual ground motion that is not detectable except with very careful measurements.

Question 23

Analyses of these observations show that the North American Plate is being slowly pushed ______ and slightly ______ by the force of the subducting Juan de Fuca plate. However, the “sticky” junction between the two plates periodically slips as the stresses ______ to a point where the plates can no longer hold together. The periodic slip events appear to be _____ stress in a benign way, thus perhaps reducing the chance of a major earthquake.

However the situation may not be this simple. If stress is being regularly released in some regions of this subduction zone, there must be accompanying ____ in stress at other locations. The entire situation appears complicated, and it is currently being studied by large groups of scientists to attempt to understand better the implications on the potential of major earthquakes off the coast of the Cascadia region.

Answer 23

eastward ; upwards ; accumulate ; releasing ; increases

Question 24

Summary:

Where will earthquakes occur?

What effects can be anticipated if an event occurs?

When will an event occur?

Answer 24

At faults, but geometry and physics are complicated.

Knowing how ground moves allows us to build better buildings.

Estimating probability is more helpful than trying to forecast times. But… reliable records exist for only the past 100 years.
Other possible precursors exist… but we still need data and explanations on how these are related.