Seismic hazard on an active fault-- Xiadian fault

Institute of Mechanics Engineering ,China Earthquake Administration

Zhao Jisheng1 Introduction
 With major infrastructure projects are constructed inrecent years , for example, the south-to-north watertransfer project, west to east gas pipeline project andsome large span bridges, they inevitably can passthrough some active faults with strong activity.
Here, we focus on estimation of surface dislocationinduced by strong earthquake on an active fault in 100years, to ensure the safety of their service life.
Seismic hazard of an active fault is a basis to choiceroute line of the major projects, seismic design measures.
An example: Xiadian Fault (XD-F)

2 The Spatial characteristics of XD-F
116°

120°

118°

裂

家口-蓬郯

张庐断40°

莱断裂

带大兴

安岭

-太行山断裂带

带

XD-F

38°

XD-F is a 20km long Holocene fault, Formed in the early
Quaternary, Normal Fault, trend NNE, Tendency SE, slide in
Quaternary make Xiadian group(Q1) drop 312m,Zhaili group(Q2)drop 139m, Dongying group(Q3) 15m.

The neo-tectonic characteristics
Most part segmentof XD-F located in
the north China
plain fault block,the other in
Yanshan fault
block. On thesecondly stege, it
located on theboundary of Daxin
uplift block andJizhong depression
block, where adisastrous
earthquake Ms8
took place in 1679.
UpliftDepression

116°

120°

118°

裂

家口-蓬郯

张

庐

断

40°

莱断裂

带大兴

安岭

-太行

山断

裂带

带XD-F

38°

fau
considered the width of fault zones. XD-F and several faults inparallel are almost orthogonal to Zhangjiakou-Penglai fault zone.

The fault system feature -Small scale

In small area, XD-F, SL-F
and HG-F are almost
orthogonal to NankouSunhe fault(NS-F).
NS-F is a blind fault,
which control MachikouShahe depression
boundary. Starting from
Nankou along SE
direction to Sunhe,length is about 58km.
Trench survey showed, it
is a Holocene Active fault.

Figure 3 D

maoctonic

XD-F can be divided into
4 different activities ofthe fault segment. TheXiadian segment is aHolocene fault about28km, which controlled
the boundary of Dachangbasin.

GPS and tectonic stress direction

GPSPrincipal stressdirectionDangerous area

The application of GPS,tectonic stress field,
mechanics parameters ofRock, soil and the fault
fracture zone, we can use
numerical fine-analysis
method, or the coarse
blocks analysis method,
give some positions ofstress changed
Significantly, where may
be an earthquake takeplace3 The earthquake sequence
region of interestEarthquake record on the XD-fault-- Earthquake catalogue M≥4.7
since the beginning of thehistory-- Earthquake catalogue
2.0≤Ms≤4.6 1970～2011.10
The earthquake records of XD-fault

Distribution of earthquakes on XD-faultTemporal distribution of earthquake on the XD-fault

Magnitude-frequency relation of earthquakes on the XD-fault

So short atime
earthquake
record;So limited thenumber ofearthquakes.

Comparison diagrams of GR relation

The paleo-earthquakes on the XD-fault

Location oftrenching

Distribution of paleo-earthquakes on XD-fault

Xiang Hongfa (1988), Ran
Yongkang (1998) had been
excavated trench of the fault
characteristics to chick paleoearthquakes. Xu Xiwei (2002)
used the drilling data, by using
the successive limit method to
get 4 paleoseismic events on
XD-F in period of Holocene.
They are 1679 (Sanhe-Pingu
earthquake), (4.2+0.37) Ka,(7.3+0.3) Ka and (11.9+2.2)
Ka, recurrence interval of
about 3.1-4.6ka. The
corresponding magnitude 7.55,7.45, 7.32, 8.

Temporal distribution with paleo-earthquakes on the XD-F

There existed
an interval ofcharacteristics
earthquake,but the record
is incomplete inany oneinterval.

4 Assessment of seismic hazard on XD-F--On the XD-fault earthquake recurrence model is quasiperiodically recurrence.

--The trench information verify that strong earthquake interval is3.1-4.6ka.

--Using state variable of rate and state dependent friction law in XDF,its interval is the average 0.85-0.95 times.

The characteristic earthquake model--Characteristic earthquake with a magnitude of 7.5, atintervals of 3450 * 0.85 = 3000 years.
--1679 Ms8 earthquake elapsing time is 332 years, thenext 100 years Xiadian fault will not 7.5 earthquakeoccurred.

The model of Gutenberg-Richter model
Earthquake catalogue M≥4.5 since the first record in the history

Defect: Because of statistical range is small (wedefined) and earthquake recorded time history is short.

Strain energy accumulation model base on characteristic
earthquake quasi-period
Characteristic
earthquake on XDF is Ms7.5,
intervals is about3000 years.

Comparison diagrams of zonation map

1679’s earthquake
elapsing time is332 years,
The next 100 years( i.e. passing timeof 432 years ) themaximum
earthquake on XDF Will be Ms6.4,
according to thestrain energy
accumulation mode
spacing.

5 Estimation of surface rupture inducedby earthquake on XD-F in the next 100years

Strain energy accumulation model base on characteristic
earthquake quasi-period (A step memory model) used,
Assume epicenter in the fault is random distribution, elapsed
time is t0 = 432 years, pipelines location 1, 2 crossing thefault larger than the dislocation of D annual exceeding
probability p (d) iswell’s statistical relation

Dengqidong’s statistical relation

6 Conclusion
Using data of geological region around XD-F, GPS, tectonic
stress field, we can find some dangerous areas where anearthquake would be taken place.

Because we confined statistical area is small, the number ofEarthquake is limited, paleo-earthquake trench explorationis needed.
Characteristic earthquake model, Gutenberg-Richter model,
and Strain energy accumulation model based on
characteristic earthquake quasi-period can be adopted in
the seismic hazard assessment from the characteristics offault. XD-F belongs the third.

Surface rupture from earthquake on XD-F is evaluated in
the next 100 years.

Thank youquestions and suggestions?