# Presentation: 085810

## GPS Requirements for Tsunami DetectionY. Tony Song & Geoff Blewitt

**Collaborators:****Yoaz Bar-Sever, Richard Gross, Vindell Hsu, Kenneth Hudnut, Hans-Peter Plag ,****Mark Simons, and Frank Webb**
** **
**Jet Propulsion Laboratory ****NOAA (PTWC)**
**USGS **
**Caltech **
**University of Nevada Reno**

## Tsunami Basics

- Tsunamis are usually caused by undersea earthquakes.
- Tsunami waves travel at a speed of ~800 km/hour (or 200 m/s) in deep oceans.
- A meter-height tsunami in the deep ocean can grow to tens of meters at coast.
- Unlike wind-driven ocean waves that are only a disturbance of the sea surface, the tsunami wave energy extends to the ocean bottom.

- 2004 Indian Ocean Tsunami

- _Tsunamis occur after earthquakes_

## Recent Tsunami Events

_**Conclusion:**_** Earthquake magnitude does not determine tsunami impact.**

| Date | Location | Magnitude | Early Warning? | Fatalities |
| --- | --- | --- | --- | --- |
| 26 Dec 2004 | Sumatra | 9.2 | No | Tsunami death~230,000 |
|   28 Mar 2005
19 July 2005 | Nias Island
North California | 8.7
7.7 | Panic evacuation
False alarm | Evacuation killed ~100
No tsunami |
| 27 Jan 2006
3 May 2006
19 July 2006
15 Nov 2006 | Benda Sea
Tonga
South Java
Kuril Islands | 7.6
8.0
7.7
8.3 | ?
False Alarm
No
False alarm/alert | No tsunami
No tsunami
Tsunami death~730
Small tsunami |
|  13 Jan 2007
1 Apr 2007
15 Aug 2007
12 Sep 2007 | Kuril Islands
Solomon Island
Central Peru
South Sumatra | 8.1
8.0
8.0
8.4 | False alarm/alert
No
Alert
Alert | No tsunami
Tsunami death~54
No tsunami
No tsunami |

**Recent Tsunami Events**

- 11 events in 4 years

## The Consequence of Late Warnings 

**The Consequence of Late Warnings **

- 2004: tsunami death ~230,000
- 2006: tsunami death ~730
- 2007: tsunami death ~54

## The Consequence of False Alarms

**The Consequence of False Alarms**

**State of Hawaii’s estimation: an evacuation from a tsunami alarm would have cost the state $58.2 million in economic losses (Eddie Bernard, 1996).**

**Since 1982, tsunami warnings based on earthquake magnitude have produced false alarms 16 out of 16 in Pacific (U.S. Government Accountability Office, GAO-06-519).**

- Panic evacuation killed ~100 in March 2005

## Earthquakes Occur Near Coast

## This talk is based on:

- Song, Y. T., Detecting tsunami genesis and scales directly from coastal GPS stations, *GRL*, **34**, doi:10.1029/2007GL03168 (2007).

_**Tsunami Theory**_
- Song et al., Horizontal impulses of faulting continental slopes dictate tsunami genesis, *Ocean Modell.*, doi:10.1016/j.ocemod.2007.10.007 (2008)

_**Seismic inversion Approach**_
- Song et al., The 26 December 2004 tsunami source estimated from satellite radar altimetry and seismic waves, *GRL*, **32**, doi:10.1029/2005GL023683 (2005).

***This talk is based on:***

_**GPS Approach**_
- Blewitt, G., et al. Rapid determination of earthquake magnitude using GPS for tsunami warning systems. *GRL*, **33**, L11309, doi:10.1029/2006GL026145, (2006).

## 1. Tsunami Genesis

**1. Tsunami Genesis**

_**Tsunami Theory**_
*Those earthquakes **	**    transfer **	**    oceanic energy*

- Knowing how tsunamis are generated by earthquakes is the key to successful prediction.

**Lateral motions of continental slopes are the main source of tsunami energy**

**Notes:**
The proposed method is based on previous studies.

## In the Sumatra Tsunami Case

**In the Sumatra Tsunami Case**

**Lateral motions of continental slopes are the main source of tsunami energy**
**potential energy = 1 (vertical)**
**kinetic energy = 5 (horizontal)**

**Notes:**
The proposed method is based on previous studies.

## 2. Developing the GPS Method

_**Step 1:**_**	****GPS displacements**
_**Step 2:**_**	****Seafloor displacement**
_**Step 3:**_**	****Tsunami energy**

**Calculating tsunami source energy from GPS displacements**

**Notes:**
The key is to get the undersea ground motions.

## Using estimated orbits
Rapid displacement
Data confirm that it arrives mostly with body waves
Can be resolved using 15-minutes after the quake
Accuracy ~ 7 mm
Can be used to estimate earthquake slip model
Model displacements ~ 3 mm
And keep in mind...
Network was far from optimal

- Using estimated orbits
- Rapid displacement
- Data confirm that it arrives mostly with body waves
- Can be resolved using 15-minutes after the quake
- Accuracy ~ 7 mm
- Can be used to estimate earthquake slip model
- Model displacements ~ 3 mm
- And keep in mind...
- Network was far from optimal

**GPS 30-sec Series**

_**Step1:**_** GPS Displacements**

## Step2: Seafloor Displacement

- Seafloor motions derived from GPS data

_**GPS-inverted Seafloor Displacements**_

**Notes:**
Examples

## Step3: Determining Tsunami Scales

**Earthquakes—Richter’s scale (magnitude)**
**Hurricanes—Simpson’s scale (category)**
**Tsunamis can be scaled (****based on ****sqrt (*****E******T*****)**** ~ tsunami height****):**

**If**** *****S******T****** < 5, *****local warning only.**
**If *****S******T****** > 5, *****basin-wide warnings and modeling are needed. **
**Early warnings can be issued in ****few minutes after quake****.**

| Earthquake Magnitude | Tsunami Energy
(ET) |  | Tsunami Scale
(ST) |  | Basin-wide Warning? |
| --- | --- | --- | --- | --- | --- |
|  | GPS |  | GPS |  | ST = 5 threshold |
| 2004 Sumatra (Mw 9.2) | 6.0e+15 J |  | 5.8 |  | >> 5   Yes |
| 1964 Alaska (Mw 9.2) | 8.2e+15 J |  | 5.9 |  | >> 5   Yes |
| 2005 Nias (Mw 8.7) | 2.8e+14 J |  | 4.4 |  | << 5   No |

**Notes:**
Tsunami scales are more accurate than earthquake magnitudes.

## Summary: Tsunami Prediction System

**seafloor motions**

**Tsunami scales**

- GPS

**3-D Ocean Model**

**Notes:**
For the first time, we have successfully developed a coupled earthquake-inversion and OGCM model.

## From Historical Tsunamis to GPS Requirements

## From Historical Tsunamis to GPS Requirements

- 1m

- 5 cm

- 200 km

- 200 km

- Tsunami height

- GPS displacement

## NASA Decision Project: GPS-aided Real-Time Earthquake and Tsunami (GREAT) Alert System--Bar-Sever et al

**Existing GDGPS (JPL/NASA)**

**Add into GDGPS**

**Coastal Real-Time GPS Network**

_**Technical Requirements:**_
**Network design (~10 km spacing)**
**Signal frequency (1 Hz)**
**Data accuracy (< 1 cm) **
**R/T GPS orbits and clocks (10 sec)**
**Data processing ( 2 min)**
**GPS-inversion seafloor displacement & tsunami energy estimation (2 min)**
_**Logistical Requirements:**_
**International collaboration**
**Systems integration**