Dynamic Triggering Semi-Volcanic Tremor in Japanese ... · Dynamic Triggering Semi-Volcanic Tremor in Japanese Volcanic Region 2 Figure 1. The map of Japan. The High Sensitivity Seismograph

HY.SUetal.:DynamicTriggeringSemi-VolcanicTremorinJapaneseVolcanicRegion

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Dynamic Triggering Semi-Volcanic Tremor in Japanese Volcanic Region by The 2016 Mw 7.0 Kumamoto Earthquake

Heng-Yi Su1*, Aitaro Kato2

1Department of Earth Sciences, National Central University, Taoyuan City, Taiwan, R.O.C

2Earthquake Research Institute, University of Tokyo, Tokyo, Japan

Abstract Semi-Volcanic Tremor is a non-impulsive deep seismic signal detected in the volcanic region.

It has been identified by previous studies that the 2004 Sumatra Earthquake and the 2011

Tohoku-Oki Earthquake triggered the semi-volcanic tremors in the Hokkaido. These trig-

gered tremors are roughly located at epicenters of ambient tremors Therefore, we download-

ed the seismic data from Hi-net and V-net and examined whether the 2016 Kumamoto earth-

quake triggered the semi-volcanic tremor. After data analysis, we detected a burst of tremors

triggered during the passage of surface waves at the central Hokkaido, which is slightly

western and deeper than the location determined by the previous study. Furthermore, the

triggered tremor is more relative to the Love wave and we infer the temporal shear stress

loading caused by Love wave deformation prompted fractures of some pre-existing faults

those might be weakened by infiltration of fluids expelled from the underneath magmatic

body. Repetitive stress loading leaded to an excitation of a burst of low-frequency earth-

quakes.

1. Introduction Recently, the research of the triggered

tremor is a good way to help us to better

understand the physical mechanism of the

earthquake. Knowing the mechanism be-

tween earthquakes can help us to improve

the early warning system and the seismic

hazard analysis. The dynamic triggering

earthquake is well known in the volcanic

and geothermal regions, which have the

high background earthquake activities or the

fault on the boundary of the plates (Hill et

al., 1993). Recently, some studies found that

we can still detect the signal of triggered

earthquake in the relatively stable intraplate

region (Gomberg et al., 2004). Moreover,

long-period non-volcanic tremor was found

and located along the subduction zone in

southwest Japan (Obara, 2002). We can also

identify the similar non-volcanic signal in

the volcanic region (Obara, 2012; Chao and

Obara, 2016). Based on the previous study,

there are some triggered regular earthquakes

have been detected after the Kumamoto


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Figure 1. The map of Japan. The High Sensitivity Seismograph Network (Hi-net) and the

V-net operated by the National Research Institute for Earth Science and Disaster Prevention�NIED�of Japan are shown as black crosses and blue circles. The red triangles represent the

active volcano near the V-net.The inset shows an enlarged view of the rectangle with epi-

center and focal mechanism of the 2016 Kumamoto earthquake.

earthquake and we can find that there are

some high frequency components in the

waveform from the study (Enescu et al.,

2016). Therefore, we are going to investi-

gate that whether we can identify the trig-

gered tremor by the Kumamoto earthquake

or not and explain the mechanism of the

triggered tremor if we find the

semi-volcanic tremor. Furthermore, people

inferred the triggered events are more cor-

related to Rayleigh wave in western of japan

(Miyazawa et al., 2008). However, the

tremor found in Taiwan was triggered by

Love wave (Peng and Chao, 2008). There-

fore, we will examine the correlation be-

tween the triggered tremor we found in

Hokkaido and the surface wave.

2. Observation In this study, we used the seismic data rec-

orded by the V-Net, and by the High Sensi-tivity Seismograph Network�Hi-Net�which


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Figure 2. We can see the clearly Love wave on transverse component. After applying the fil-

ter, the tremor triggering by the Love wave is clearly visible during the 800 seconds to 1200

seconds. The bottom picture is to plot the frequency component of the transverse wave with

0.5 Hz low-pass filters.

are both operated by the National Research

Institute for Earth Science and Disaster Prevention�NIED�of Japan. We have

processed the seismic data from the short

period seismometer of V-Net. To identify

triggered tremor, we utilize the Butterworth

band-pass filter in the frequency range of 2

to 8 Hz, which is the dominant frequency

components of triggered tremor, and search

for the bursts of non-impulsive seismic sig-

nal. In order to correlate the triggered trem-

or with the surface waves, we first removed

the instrument response, then using the filter

under the frequency range of 0.01 to 0.2 Hz

to the broadband seismic data. The triggered

tremor is often well correlated to the surface

waves passing. That is to say that after we

remove the dominant frequency component

of the surface waves, we can see the

low-frequency earthquake phenomena af-

terwards. Therefore, we might see the peak

of the triggered tremor that is relative to the

phase of surface waves. Figure 2 shows the

surface wave compared with the seismo-

gram filtered by band-pass filter in 2 to 8 Hz

recorded by the V-net station TKOV.In the

spectrogram we can clearly see the fre-

quency components of triggered tremor

during the 800s to 1200s, of which ampli-

tudes extend up to around 10 Hz.

3. Tremor Location After detecting the triggered tremor, we

picked the S wave arrival time of each burst


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Figure 3. Observations of triggered tremor and ambient tremors in the volcanic region of

central Hokkaido. The green circle is the triggered tremor detected in this study. The white

circle is the triggered tremor detected in the previous study. The diamonds are the location of

different bursts in the tremor. The yellow circles are the ambient low-frequency earthquakes

determined by the JMA. The red triangle is the active volcano. The inverted triangles are the

V-net station and the purple inverted triangles are the station we used to locate the triggered

tremor. The crosses are the stations of Hi-net and the red crosses are the station we used to

locate the triggered tremor. Color bar shows the time sequences of different bursts of earth-

quake.

of the low-frequency earthquake and uti-

lized the different travel time between dif-

ferent seismic stations to locate the triggered

event. Figure 3 shows triggered tremor hy-

pocentral distribution and the error of depth

is within 10 km. The result was calculated

from five Hi-net stations and two V-net sta-

tions. The triggered tremor source is located

at 142.6863°E, 43.1753°N and 26 km depth.

Comparing with previous study (Chao and

Obara, 2016), ours is deeper. Also, we shift

the bursts of the triggered tremor back to the

source region. We use the record of stations

TKOV and shift the time with 10.72s, which

is computed by Taup (Crotwell et al., 1999).

In Figure 4, we want to determine the rela-

tionship between the surface wave and trig-

gered tremor. If the triggered tremor is sen-

sitive to the change of the stress field, it will

be well correlate to each surface wave phase.


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Figure 4. Correlating the Rayleigh wave and Love wave with triggered tremor. The upper and

middle waveforms are under 0.01 to 0.2 Hz filter and represent Rayleigh wave and Love

wave, respectively. The lower waveform is filter by band-pass 2 to 8 Hz and we can clearly

see the tremor signal. We shifted each burst of low-frequency earthquake back to the tremor

source region and correlated the peak of both Rayleigh wave and Love wave to triggered

tremor.

Figure 5. Depth section of the P-wave velocity structure superimposed with triggered and

ambient tremors. A low-velocity body is imaged beneath these tremors.

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Here the Love wave is more in phase with

tremor bursts and the amplitude of Love

wave is also larger than Rayleigh wave,

suggesting that the tremor might be trig-

gered by the Love wave.

4. Discussions and Conclusion We verify the triggered tremor source in the

region of the deep volcanic low-frequency

earthquake in central Hokkaido (Obara,

2012; Chao and Obara, 2016). Nevertheless,

the depth of the triggered tremor source in

this study is greater than previous one (Chao

and Obara, 2016). Also the average depth of

the triggered tremor is greater than most of

the ambient tremors. Yet, the determination

of depth still need more evidences (different

method) to support it. The deep

low-frequency earthquakes occur near the

low-velocity zone (Hasegawa et al., 2009;

Obara, 2012). In this study, our research

focuses on the volcanic region, and the

low-frequency tremor we detected might be

adjacent to the magma body. In addition, the

tremor is more correlative to the Love wave.

This correlation result indicates that the

temporal shear stress loading caused by

Love wave deformation prompted fractures

of some pre-existing faults those might be

weakened by infiltration of fluids expelled

from the underneath magmatic body. Repet-

itive stress loading leaded to an excitation of

a burst of low-frequency earthquakes. Fig-

ure 5 shows that there is a low-velocity zone

beneath the ambient tremors and the trig-

gered tremors, which is more likely a mag-

matic body or other fluid body.

5. Acknowledgement We thank the NIED provides the great and

high quality seismic network data and the

JMA provides the seismic catalog. The fig-

ures in this study were created by using the

Generic Mapping Tools, SAC and

MATLAB. The data processing was done in

the Earthquake Research Institute and su-

pervises by Prof. Aitaro Kato. Also, I ap-

preciate to the help from Dr. Kevin Chao

when he was in his short-term visiting in

ERI.

6. Reference1. Chao, K., & Obara, K. (2016). Triggered

tectonic tremor in various types of fault

systems of Japan following the 2012 Mw8.

6 Sumatra earthquake. Journal of Geophys-

ical Research: Solid Earth, 121(1), 170-187.

2. Crotwell, H. P., T. J. Owens, and J. Ritsema

(1999). The TauP Toolkit: Flexible seismic

travel-time and ray-path utilities, Seismo-

logical Research Letters 70, 154–160.

3. Enescu, B., Shimojo, K., Opris, A., & Yagi,

Y. (2016). Remote triggering of seismicity

at Japanese volcanoes following the 2016

M7. 3 Kumamoto earthquake. Earth, Plan-

ets and Space, 68(1), 165.

4. Gomberg, J., Bodin, P., Larson, K., &

Dragert, H. (2004). Earthquakes nucleated

by transient deformations—a fundamental

process evident in observations surrounding


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the M7. 9 Denali Fault earth-

quake. Nature, 427, 621-624.

5. Hasegawa, A., Nakajima, J., Uchida, N.,

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7. Miyazawa, M., & Brodsky, E. E. (2008).

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8. Peng, Z., & Chao, K. (2008). Non-volcanic

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Dynamic Triggering Semi-Volcanic Tremor in Japanese ... · Dynamic Triggering Semi-Volcanic Tremor in Japanese Volcanic Region 2 Figure 1. The map of Japan. The High Sensitivity Seismograph