Auxiliary Materials for
A mid-crustal ramp-fault structure beneath the Taiwan tectonic wedge illuminated by the 2013
Nantou earthquake series
Ray Y. Chuang 1* , Kaj M. Johnson 1 , Yih-Min Wu 2 , Kuo-En Ching 3 , and Long-Chen Kuo 4
1: Department of Geological Sciences, Indiana University, Bloomington, Indiana, USA
2: Department of Geosciences, National Taiwan University, Taipei, Taiwan
3: Department of Geomatics, National Cheng Kung University, Tainan, Taiwan
4: Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan
The supplementary materials include five figures and three tables. The first figure shows vertical
GPS data used in the inversions. The second figure shows posterior probability distributions for the homogeneous models of the two main shocks. The third figure shows model fits to the vertical GPS data. The forth figure compares coseismic slip distribution and depths between the homogeneous model and two layer models of the two main shocks. The fifth figure demonstrates a cross-section across the central Taiwan, showing that the Nantou fault plane could match the
Shuilikeng fault at depth based on the structure profile of Brown et al. [2012] and supporting the first possible interpretation of the structural architecture in the paragraph 4.3 of the main text.
The first table summarizes all model parameters estimated in the homogeneous and layer models.
The second and third tables summarize earthquake parameters for the two main shocks from several catalogs.
Figure S1.
Vertical coseismic displacements of the March 27 (blue) and June 2 (red) Nantou earthquakes. Fault traces based on Shyu et al. [2005b] and Brown et al [2012]. The red beach balls are Nantou main shocks and black beach balls are Chi-Chi aftershocks and other M
L
>5.5 events. Blue and orange dots are seismicity before and after Chi-Chi earthquake, respectively.
Cyan and magenta dots are aftershocks of the March 27 and June 2 events, respectively. CHF:
Changhua fault; CLPF: Chelungpu fault; STF: Shuangtung fault; SLKF: Shuilikeng fault; TLF:
Tili fault; LSF: Lishan fault.
Figure S2.
(a) Posterior probability distributions for the homogeneous model of the (a) March 27 earthquake and (b) June 2 earthquake. Red lines indicate mean values. Sigma 1 and 2 are data weighting values for horizontal and vertical GPS data, respectively.

Figure S3.
Coseismic slip distribution and model fit for the homogeneous model of the (a)
March 27 earthquake and (b) June 2 earthquake. Blue arrows are vertical observations and red arrows are model vectors. Error ellipses show 95% confidence level.
Figure S4.
(a) Comparison of slip distribution between the homogeneous and two layered models for the March 27 earthquake. The red dots indicate main shock hypocenter and grey dots indicate aftershocks. (b) Comparison of model plane depth between the homogeneous model and two layered models for the March 27 earthquake. (c) Comparison of slip distribution between the homogeneous and two layered models for the June 2 earthquake. (d) Comparison of model plane depth between the homogeneous model and two layered models for the June 2 earthquake.
Figure S5.
Central Taiwan cross-section showing the Nantou fault. Structural profile follows
Brown et al. [2012] and the p-wave velocity tomography image is from Kuo-Chen et al. [2012].
Black dots are background seismicity from 1991 to 2009. Other symbols same as Figure 1b.