Slow slip events observed days before and close to the 2001 Mw7.8 Kokoxili earthquake in northern Ti...
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Slow slip events observed days before and close to the 2001 Mw7.8 Kokoxili earthquake in northern Tibet. Zhengkang Shen & Huaizhong Yu. Outline. Tremor and slow slip events observed around circum-Pacific plate boundaries 2001 Mw7.8 Kokoxili earthquake

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Zhengkang shen huaizhong yu

Slow slip events observed days before and close to the 2001 Mw7.8 Kokoxili earthquake in northern Tibet

Zhengkang Shen & Huaizhong Yu


Outline

Outline

  • Tremor and slow slip events observed around circum-Pacific plate boundaries

  • 2001 Mw7.8 Kokoxili earthquake

  • Tremor events observed prior to the Kokoxili earthquake

  • Source location determination

  • Results


Zhengkang shen huaizhong yu

From Roger and Dragert, Science, 2003


Zhengkang shen huaizhong yu

Dragert et al., Science, 2001


Zhengkang shen huaizhong yu

Kosklodotov et al., GRL, 2003


Source location determination

Source location determination

  • High-pass filter the data;

  • Take RMS of the data;

  • Smooth the data with 10-sec window;

  • Correlate the data envelopes to find event onset differences;

  • Use the onset differences to determine the source


Zhengkang shen huaizhong yu

Kao et al., JGR, 2006


Source location determination1

Source location determination

  • High-pass filter data

  • evaluate “brightness” through space ηand time τover all station records Un

  • Search for maximum of “brightness”


Zhengkang shen huaizhong yu

Dec 2000 – Dec 2003, 10 clusters of tremor events, frequency 1-10 Hz, located depth 20-40 km along SAF south of Parkfield

Nadeau, Science, 2005


Zhengkang shen huaizhong yu

2001/11/14 Mw7.8 Kokoxili earthquake


Zhengkang shen huaizhong yu

Left surface slip measured by field geology. Color code: Red, field measurements by J. Chen, Institute of Geology, CSB; Black, measurements by X. Xu, Institute of Geology, CSB; Green, measurements by G. Dang, Qinghai Seismological Bureau.


Zhengkang shen huaizhong yu

Yang et al., Seismol. Frontier, 2003


Zhengkang shen huaizhong yu

HTG花土沟

GOM格尔木

WUS乌什

WMQ乌鲁木齐

WEQ温泉

KEL库尔勒

KSH喀什

HTA和田

GTA高台

FYN富蕴

AXX安西

2001/11/10

2001/11/11

2001/11/12

2001/11/13


Zhengkang shen huaizhong yu

Data of 2001/11/11 after 0.1-0.2 Hz band-pass filtering


Zhengkang shen huaizhong yu

Envelops of amplitude-square with 10 sec smoothing


Envelop

envelop

data


Event source relocation

Event Source Relocation

  • Assuming tremors are primarily direct S waves, select a reference station, calculate correlations of station pairs with a time window of 100 sec and a moving offset; keep the ones with correlations > 0.8 in general and > 0.7 for stations far away from each other.

  • Using the differential arrival times as input, invert for event hypocenters using the HYPOSAT software with a 1-D S-wave velocity model of northern Tibet (Zhang et al., 2000).

  • Compute travel time postfit residuals, remove the ones > 10 sec, and repeat the last step.

  • Retain the events with ≥8 (out of 11) stations remained in the inversion process.


Zhengkang shen huaizhong yu

locked

depth

transition

creeping

mantle

longitude


Zhengkang shen huaizhong yu

HTG

GOM

AXX

KEL

WMQ

GTA

HTA

WUS

FYN

WNQ

KSH


Zhengkang shen huaizhong yu

HTG

GOM

KEL

AXX

HTA

WMQ

GTA

WUS

WNQ

FYN

KSH


Zhengkang shen huaizhong yu

HTG

KEL

GOM

HTA

AXX

WMQ

WUS

GTA

WNQ

FYN

KSH


Zhengkang shen huaizhong yu

HTG

GOM

KEL

HTA

AXX

WMQ

WSH

GTA

WNQ

KSH

FYN


Zhengkang shen huaizhong yu

HTG

GOM

AXX

KEL

GTA

WMQ

HTA

WUS

FYN

WNQ

KSH


Zhengkang shen huaizhong yu

HTG

GOM

KEL

AXX

HTA

WMQ

GTA

WUS

WNQ

KSH

FYN


Zhengkang shen huaizhong yu

HTG

GOM

KEL

AXX

HTA

WMQ

GTA

WUS

WNQ

KSH

FYN


Zhengkang shen huaizhong yu

Conclusion?Slow slip hypocenters are found to scatter in a region of 88.0-91.0oE, 34.5-37.5oN, seem to indicate that their locations are close to the epicenter of the Kokoxili earthquake. Moreover, the depths of these events fall within the range of 10 – 40 km, suggesting that slow slip events probably occurred in the brittle-ductile transition zone on or near the East Kunlun fault. The failure at the transition zone might have increased the Coulomb stress at the hypocenter and finally triggered the Mw 7.8 earthquake.


Zhengkang shen huaizhong yu

格尔木GOM

喀什KSH

和田HTA

乌鲁木齐WMQ

高台GTA

花土沟HTG

乌什WUS

安西AXX

银川YCH


Zhengkang shen huaizhong yu

XAN


Zhengkang shen huaizhong yu

ARU


Zhengkang shen huaizhong yu

AAK


Zhengkang shen huaizhong yu

WMQ


Zhengkang shen huaizhong yu

Cascadia, Canada

τupdip

ΔCFS

τstrike

σ


Zhengkang shen huaizhong yu

Shen et al., BSSA, 2005


Zhengkang shen huaizhong yu

昆仑山口西M8.1地震发生前的慢地震事件

Kazushige Obara, 2002,Nonvolcanic Deep Tremor Associated with Subduction in Southwest Japan,Science, 296,1679-1681

日本西南俯冲带慢地震事件

频率范围:0.5 ~ 5 Hz

求包络线方法,得到不同波形序列相关性> 0.9,波形

认为是同一慢地震事件

Honn Kao, et al. 2005. A wide depth distribution of seismic tremors along the northern Cascadia magin, Nature, 436(11), 841 ~ 844.

卡斯卡底俯冲带慢地震事件

频率范围:1 ~ 5 Hz

Brightness function方法根据频率、振幅,找到对应的慢地震事件


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