Earthquake Swarm Activity in Changbaishan Tianchi Volcano

Abstract

In summers of 2002 and 2003, temporary seismic stations had recorded a large number of small earthquakes and a series of swarms near Changbaishan Tianchi volcano. Earthquake location result shows that these earthquakes mainly occurred near the Tianchi caldera. Almost all swarms were concentrated at southwest of the caldera, and no swarms occurred in northeast area where earthquakes densely concentrated. In other seasons, the permanent station CBS is the only seismic station to monitor volcanic earthquakes in Tianchi volcano. Waveform correlation analysis of seismic data recorded at CBS in different time shows that earthquake swarms occurred in other seasons also concentrated in the southwest Tianchi Lake. High‐precision relative location shows that hypocenters of earthquake swarm distributed along northwest with a dip angle of 80° to southwest. During the July 13, 2003 earthquake swarm the hypocenters migrated from deep to shallow and deeper events had upward first motion directions almost at all stations. That means they had obvious expansion component in source mechanism. Taking into account of significant surface deformation in Changbaishan Tianchi volcano since 2002, geochemical anomalies and harmonic‐spectral earthquakes, we believe that the earthquake swarm activity was caused by magmatic and hydrothermal activity and pressure increase of magma near the depth of 5km.

An overview of recent (1988 to 2014) caldera unrest: Knowledge and perspectives

“…In the 2002-2006 period, the number of earthquakes increased to 72 per month, accompanied by earthquake swarms and harmonic events. The seismicity peaked in November 2003, with 243 seismic events clustering beneath the NE and SW parts of the caldera, at a depth of~5 km [Wu et al, 2005[Wu et al, , 2007Xu et al, 2012]. A maximum uplift of 68 mm between 2002 and 2005 was detected on the northern caldera rim, related to the addition of magma in a reservoir at 2 to 6 km of depth below the summit, in agreement with the location of earthquake swarms [Xu et al, 2012;Wei et al, 2013;GVP report, 08/2010 (BGVN 35:08)].…”

Quantifying gas emissions from the “Millennium Eruption” of Paektu volcano, Democratic People’s Republic of Korea/China

“…This corresponds to a magma chamber depth between 0.5 and 3.5 km, assuming an average crustal density of 2.4 g/cm 3 . Note that the maximum magma chamber depth of 3.5 km is consistent with seismicity recorded during the 2002–2005 period of seismic unrest at Paektu ( 34 ). …”

Application of satellite thermal infrared remote sensing in monitoring magmatic activity of Changbaishan Tianchi volcano

“…This suggests about 10 times increase in seismic intensity. After August 2005, the frequency of earthquakes declined sharply, and returned to the normal level as before June 2002 [14].…”

“…The observational results in recent ten years show that the volcanic activity of Tianchi volcano varies year by year. The microseism frequency increases from 32 in 1999 to 469 in 2002 [13], and then the number of earthquake increases dramatically after June 2002 and reaches the peak in 2004 with the frequency as ten times as in 1999 [14]. The ground deformation observed from GPS survey displays a typical radiation movement pattern with center at the crater lake, and leveling measurements also reveal a rapid uplift around the caldera lake [15,16].…”

“…These activities can be detected by various monitoring methods with annual interval of observation. Currently, the monitoring methods applied in Tianchi volcano, including seismological monitoring [13,14], horizontal ground deformation from GPS observation [15,16], vertical ground deformation from leveling measurement [15], and variation of isotope 3 He/ 4 He ratio from gas geochemistry monitoring, are performed once in a year. Therefore, it is reasonable to believe that one can use a series of remote sensing images from different years which are composed with one single image per year to study the annual magmatic activities in Changbaishan Tianchi volcano.…”