GPS observation and modeling in Taiwan

1993-1999
Hsu et al. (2009)

Ruey-Juin Rau and Kuo-En Ching
National Cheng Kung University, Tainan, Taiwan

1Outlines:
1. Why strain rate matters in earthquake
forecasting?
2. What is the current status of Taiwan
strain rate and deformation model?

2Why strain rate matters in earthquake
forecasting?
Strain rate reflects elastic stress buildup and effects
change in rheology. Help for earthquake forecast?

Consider 1.5 x 10-6/year strain rate for the major
thrusts and 3 x 10-5 ~ 3 x 10 –4 typical coseismic straindrop, the recurrence intervals for large earthquake in
Taiwan are 20-200 years.
3What is the current status of Taiwan
strain rate and deformation model?

4Taiwan Tectonic Model

Kinematic models of Taiwan arc-continent collision

Crespi, 1996

Teng et al., 2005

Geology of Taiwan
Major seismogenicstructures
1. Ryukyu trench system
2. Manila trench system
3. Frontal and out‐ofsequence thrusts
This is plate boundary!
4. Reactivationof pre‐existing structures

Tectonics and large earthquakes in Taiwan

台灣地區近三百年來重大災害地震
地震儀器記錄時期

10000

死亡人數

1000

嘉義(7.1)
台南(6.5)100

彰化(7.1)
台中 台南(6.0) (7.0)
基隆
(7.0)
花蓮 嘉義
(7.7) (6.5)

花蓮(7.5)11700

36921750

1 11 51800

3 4 4 6 6 8 8
9 5 8 2 7 1 2

1850
年代

中埔
(7.1)
新化(6.1) 白河
花東 (6.3)(7.3)

斗六(6.1)南投(6.8)苗栗台東(6.2)(7.5)

10集集(7.3)

新竹-台中(7.1)
梅山
(7.1)

恆春(7.1)

0 0 1
4 6 6

3 44 55 6
5 16 19 41900

1950

花蓮(6.8)8 96 92000

Taiwan Geodetic Network~400 continuous GPS stations~1000 campaign GPS stations
Precise leveling measurements* Dense near-fault observations* Lack of stations in thehinterland and off-shore

10

Taiwan Velocity Field
GPS Horizontal Velocities

Short‐term Vertical Velocities

Long‐term Vertical Velocities

11GPS velocity fieldCampaign

12GPS Velocity Field inTaiwan

10‐35 mm/yr~60 mm/yr~82 mm/yr

3D Block Modeling Approach (Horizontal Data)
Concept of modeling interseismic velocity field (DENODE: McCaffrey, 2002)(Slip Rate Deficit)

Tectonic Block and Fault Configurations
1. Active faults (CGS and CPC)
2. Seismicity (CWB)
3. Velocity Field

Comparison of Observations and Calculations

GPS Velocity Residuals
2 = 3.3 mm/yr

Locations of Euler Poles, Block Motions, andInterseismic Slip Rates on the Faults

Long‐term Slip Rates on the Faults

Modern Tectonic Model of Taiwan

Heuret and Lallemand [2005]

Distribution of mud diapirs in SW Taiwan• Generated offshore• Stop being active onshore• Appearing inland caused byuplift and erosion

Reactivation of inland
mud diapir in thepresent-day crustal
deformation remains
unclear.

19Line 12bLine 12b

Episodic fault creep in the Tainan tableland

GPS and precise leveling network in Tainan

X210

X210

Precise levelingin Tainan
X210

X210

X210

X210

X210

X210

X210

X210

X210

Hypothetical models for the Tainan vertical motion（1）Subsidence of the foreland basin（2）Development of mud diapir（3）Fault motion

Phase I

Phase IIPhase III

Episodic fault creep in the Tainan tableland
Creeping behavior of Tainan is controlled by the combination ofsubsidence of the foreland basin, development of mud diapir, and thefault motion

GPS Velocity Field in Chiayi Area2002-2011

Profile A‐A’cross Meishan fault

campaign
GPScontinuous
GPSleveling

Profile A‐A’cross Meishan fault

campaign
GPScontinuous
GPSleveling

Profile B‐B’cross Chiuchiungkeng fault and Tachienshan fault

campaign
GPScontinuousGPSleveling

subsidence area
down to -101 mm/yr

Profile C‐C’cross Chiuchiungkeng fault and Chukou fault

campaign
GPScontinuous
GPSlevelingSummary
1. High strain rate (~1.0 x
10-6/year) for major
thrusts and shortrecurrence intervals (20200 years) for large
earthquake in Taiwan.
2. Seismogenic structures:subduction and collisionzones and reactivationsof pre-existing structures.
3. Display wide range offault-motion andearthquake spectrums.