scholarly journals Focal Mechanisms of Small Earthquakes within the Pacific Plate near the Japan Trench

2012 ◽  
Vol 64 (2) ◽  
pp. 75-90 ◽  
Author(s):  
Shoko KOGA ◽  
Yoshihiro ITO ◽  
Ryota HINO ◽  
Masanao SHINOHARA ◽  
Norihito UMINO
Keyword(s):  
Pacific Plate ◽  
Focal Mechanisms ◽  
Japan Trench ◽  
The Pacific

scholarly journals First measurement of the displacement rate of the Pacific Plate near the Japan Trench after the 2011 Tohoku-Oki earthquake using GPS/acoustic technique

2015 ◽  
Vol 42 (20) ◽  
pp. 8391-8397 ◽  
Author(s):  
Fumiaki Tomita ◽  
Motoyuki Kido ◽  
Yukihito Osada ◽  
Ryota Hino ◽  
Yusaku Ohta ◽  
...  
Keyword(s):  
Pacific Plate ◽  
Japan Trench ◽  
Displacement Rate ◽  
Acoustic Technique ◽  
The Pacific

scholarly journals A Microearthquake Study of the Plate Boundary, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Martin Everardus Reyners
Keyword(s):  
Plate Boundary ◽  
Pacific Plate ◽  
Focal Mechanisms ◽  
Phase Changes ◽  
Indian Plate ◽  
Depth Range ◽  
The North ◽  
The Pacific ◽  
Deep Activity ◽  
Set Up

<p>The seismicity, structure and tectonics of the North Island plate boundary have been studied by means of a microearthquake traverse oriented in the direction of dip of the subducted Pacific plate and stretching from southern Hawke's Bay to northern Taranaki. The geometry of the top of the Pacific plate is inferred from a band of concentrated microearthquake activity which can be identified with the crust of the plate. The Pacific plate appears to have two knee-like bends, one between the east coast and the Ruahine Range, where the top of the plate is about 25 km deep, the other below the volcanic front, where it is about 70 km deep. The shallower bend and subsequent restraightening of the plate can be related to phase changes in the plate, while the deeper bend can be related to volcanism. Composite focal mechanisms indicate that seaward of its shallower bend the Pacific plate is being loaded by the Indian plate, whereas landward of this bend the Pacific plate is sinking under its own weight. Both composite focal mechanisms and the distribution of microseismicity in the Pacific plate suggest the existence of a major discontinuity striking down the dip of the plate and passing beneath the Tongariro volcanic centre. A conspicuous lack of microseismicity in the Indian plate in the eastern North Island revealed in this study can be related to the plates being unlocked in this region. A feature of the seismicity of the Indian plate in the region of the Wanganui Basin is the concentration of activity in the 25-42 km depth range, shallower activity being largely confined to the northeast edge of the basin, near Mt Ruapehu and Waiouru. Composite focal mechanisms suggest the 25-42 km deep activity reflects stresses set up by locking and unlocking of the plates, while the shallower activity reflects local stresses related to volcanic phenomena.</p>

scholarly journals A Microearthquake Study of the Plate Boundary, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Martin Everardus Reyners
Keyword(s):  
Plate Boundary ◽  
Pacific Plate ◽  
Focal Mechanisms ◽  
Phase Changes ◽  
Indian Plate ◽  
Depth Range ◽  
The North ◽  
The Pacific ◽  
Deep Activity ◽  
Set Up

<p>The seismicity, structure and tectonics of the North Island plate boundary have been studied by means of a microearthquake traverse oriented in the direction of dip of the subducted Pacific plate and stretching from southern Hawke's Bay to northern Taranaki. The geometry of the top of the Pacific plate is inferred from a band of concentrated microearthquake activity which can be identified with the crust of the plate. The Pacific plate appears to have two knee-like bends, one between the east coast and the Ruahine Range, where the top of the plate is about 25 km deep, the other below the volcanic front, where it is about 70 km deep. The shallower bend and subsequent restraightening of the plate can be related to phase changes in the plate, while the deeper bend can be related to volcanism. Composite focal mechanisms indicate that seaward of its shallower bend the Pacific plate is being loaded by the Indian plate, whereas landward of this bend the Pacific plate is sinking under its own weight. Both composite focal mechanisms and the distribution of microseismicity in the Pacific plate suggest the existence of a major discontinuity striking down the dip of the plate and passing beneath the Tongariro volcanic centre. A conspicuous lack of microseismicity in the Indian plate in the eastern North Island revealed in this study can be related to the plates being unlocked in this region. A feature of the seismicity of the Indian plate in the region of the Wanganui Basin is the concentration of activity in the 25-42 km depth range, shallower activity being largely confined to the northeast edge of the basin, near Mt Ruapehu and Waiouru. Composite focal mechanisms suggest the 25-42 km deep activity reflects stresses set up by locking and unlocking of the plates, while the shallower activity reflects local stresses related to volcanic phenomena.</p>

scholarly journals Spatiotemporal analysis of repeating earthquakes near Porangahau, Hikurangi Margin, New Zealand

2021 ◽  
Author(s):  
Olivia Pita Sllim
Keyword(s):  
New Zealand ◽  
Cross Correlation ◽  
Slip Rate ◽  
Pacific Plate ◽  
Focal Mechanisms ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Repeating Earthquakes ◽  
The Pacific ◽  
Temporal And Spatial

<p><b>The Hikurangi subduction zone beneath the eastern North Island, New Zealand exhibits a variety of fault-slip related phenomena including tsunami earthquakes, non-volcanic tremor, low-frequency earthquakes, episodic slow slip, and repeating earthquakes. The northern Hikurangi margin hosts shallow slow-slip and is weakly coupled to shallow depths. In contrast, the southern Hikurangi margin is strongly coupled, and only deep slow-slip has been observed. The transition in coupling occurs beneath the township of Porangahau, and is an exemplary focus region for studying how this change in locking is accommodated. </b></p><p>To examine slip processes beneath Porangahau, we have constructed and analysed a catalogue of repeating earthquakes that occurred between 2004 and 2018. Repeating earthquakes are thought to re-rupture the same fault patch at different times, and thus have nearly identical waveforms, locations and magnitudes. Because repeating earthquakes represent cyclic loading, they can be used to detect temporal and spatial changes of slip-rate at depth and hence monitor how stress is transferred to seismogenic zones. </p><p>To build a catalogue of repeating earthquakes we first clustered the GeoNet earthquake catalogue by distance and correlation to identify potential repeating events. We then used a stronger cross-correlation threshold of at least 0.95 normalised cross-correlation value at three or more stations to identify repeating earthquakes from the initial clusters. This threshold was determined by our group's previous work on the northern Hikurangi margin. We identified 225 families of repeating earthquakes, with each family having two or more earthquakes in the 14-year study period from 2004 to 2018. </p><p>We carried out manual phase picking and polarity identification for the most recent event in each family and computed absolute locations, local magnitudes calibrated with moment magnitude, and high-quality focal mechanisms. For the rest of the events in each family, we conducted cross-correlation re-picking to obtain precise relative locations and relative magnitudes. With precise locations and well-constrained focal mechanisms, we determined whether the repeating earthquake families originated within the Pacific Plate, Australian Plate or on the subduction interface. Most of the families are located within the Pacific Plate, and the majority of families that originate on the subduction interface are located near the township of Porangahau. At least 220 of the 532 identified repeating earthquakes locate at the transition from strong- to weak-coupling of the subduction interface near the township of Porangahau. </p><p>A variety of slow slip events have been detected near Porangahau in the last two decades. Even though some repeating earthquakes correlate spatially and temporally with slow slip events, temporal and spatial correlations between slow slip events and repeating earthquakes are scarce and sparse. The majority of repeating earthquakes are located up-dip or down-dip of modelled slow slip patches, with very few families having spatial correlation with slow slip events. We obtained a moment-recurrence interval relationship for the catalogue of repeating earthquakes near Porangahau and compared it to the relationship obtained by Nadeau and Johnson (1998) at Parkfield, California. Finally, we computed slip-rates using the families located on the subduction interface and obtained an average slip-rate of 13 mm/yr. The insights gained from this study lay the groundwork for future work constraining processes of strain accumulation at the creeping-to-locked transition zone near Porangahau.</p>

scholarly journals Spatiotemporal analysis of repeating earthquakes near Porangahau, Hikurangi Margin, New Zealand

2021 ◽  
Author(s):  
Olivia Pita Sllim
Keyword(s):  
New Zealand ◽  
Cross Correlation ◽  
Slip Rate ◽  
Pacific Plate ◽  
Focal Mechanisms ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Repeating Earthquakes ◽  
The Pacific ◽  
Temporal And Spatial

<p><b>The Hikurangi subduction zone beneath the eastern North Island, New Zealand exhibits a variety of fault-slip related phenomena including tsunami earthquakes, non-volcanic tremor, low-frequency earthquakes, episodic slow slip, and repeating earthquakes. The northern Hikurangi margin hosts shallow slow-slip and is weakly coupled to shallow depths. In contrast, the southern Hikurangi margin is strongly coupled, and only deep slow-slip has been observed. The transition in coupling occurs beneath the township of Porangahau, and is an exemplary focus region for studying how this change in locking is accommodated. </b></p><p>To examine slip processes beneath Porangahau, we have constructed and analysed a catalogue of repeating earthquakes that occurred between 2004 and 2018. Repeating earthquakes are thought to re-rupture the same fault patch at different times, and thus have nearly identical waveforms, locations and magnitudes. Because repeating earthquakes represent cyclic loading, they can be used to detect temporal and spatial changes of slip-rate at depth and hence monitor how stress is transferred to seismogenic zones. </p><p>To build a catalogue of repeating earthquakes we first clustered the GeoNet earthquake catalogue by distance and correlation to identify potential repeating events. We then used a stronger cross-correlation threshold of at least 0.95 normalised cross-correlation value at three or more stations to identify repeating earthquakes from the initial clusters. This threshold was determined by our group's previous work on the northern Hikurangi margin. We identified 225 families of repeating earthquakes, with each family having two or more earthquakes in the 14-year study period from 2004 to 2018. </p><p>We carried out manual phase picking and polarity identification for the most recent event in each family and computed absolute locations, local magnitudes calibrated with moment magnitude, and high-quality focal mechanisms. For the rest of the events in each family, we conducted cross-correlation re-picking to obtain precise relative locations and relative magnitudes. With precise locations and well-constrained focal mechanisms, we determined whether the repeating earthquake families originated within the Pacific Plate, Australian Plate or on the subduction interface. Most of the families are located within the Pacific Plate, and the majority of families that originate on the subduction interface are located near the township of Porangahau. At least 220 of the 532 identified repeating earthquakes locate at the transition from strong- to weak-coupling of the subduction interface near the township of Porangahau. </p><p>A variety of slow slip events have been detected near Porangahau in the last two decades. Even though some repeating earthquakes correlate spatially and temporally with slow slip events, temporal and spatial correlations between slow slip events and repeating earthquakes are scarce and sparse. The majority of repeating earthquakes are located up-dip or down-dip of modelled slow slip patches, with very few families having spatial correlation with slow slip events. We obtained a moment-recurrence interval relationship for the catalogue of repeating earthquakes near Porangahau and compared it to the relationship obtained by Nadeau and Johnson (1998) at Parkfield, California. Finally, we computed slip-rates using the families located on the subduction interface and obtained an average slip-rate of 13 mm/yr. The insights gained from this study lay the groundwork for future work constraining processes of strain accumulation at the creeping-to-locked transition zone near Porangahau.</p>

Small-scale mantle convection system and stress field under the Pacific plate

1976 ◽  
Vol 13 (3) ◽  
pp. 212-217 ◽  
Author(s):  
Han-Shou Liu ◽  
Edward S. Chang ◽  
George H. Wyatt
Keyword(s):  
Stress Field ◽  
Mantle Convection ◽  
Pacific Plate ◽  
Small Scale ◽  
The Pacific
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