Focal Depth Determination for Moderate and Small Earthquakes by Modeling Regional Depth Phases sPg, sPmP, and sPn

Ma, Shengwu

doi:10.5772/27240

Cited by 8 publications

(18 citation statements)

References 8 publications

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“…The sPn phase has not been well developed for the top three records. The reason may be that the station distances were not great enough (Ma 2010). We could have modeled the differential times between the sPn and Pn phases for the other eight records; therefore, we obtained eight focal depths and used the average as the solution for the main shock.…”

Section: The Depth Of the Main Shockmentioning

confidence: 99%

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Studies on the June 23, 2010 north Ottawa M W 5.2 earthquake and vicinity seismicity

Motazedian

2012

J Seismol

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The basic parameters for the earthquake with a moment magnitude (M W ) of 5.2 on the 23rd of June 2010 have been investigated. The earthquake occurred on a hidden fault in the northwest direction about 60 km north-northeast of Ottawa in the Western Quebec Seismic Zone (WQSZ) and had a focal depth of about 21 km. The focal mechanism was a thrust type with strike in the northwest direction and dipping in the northeast direction. The relative relocations of seven larger aftershocks show that the source rupture area was about 6 km 2 . The b value of the aftershock sequence was 0.8-1.0, and the decay rate of the aftershocks was faster than normal cases. The dominant seismogenic depths are about 12 to 22 km in most parts of the WQSZ, while the seismogenic depth along the Ottawa-Bonnechere Graben can be as deep as 28 km. Based on the seismic activity in the WQSZ and vicinity since 1961, it seems that the periods of moderate earthquakes are about 6-10 years.

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Section: The Depth Of the Main Shockmentioning

confidence: 99%

“…In this research work, we obtained the focal depth of the main shock using the RDPM method (Ma 2010). The main shock generated all three regional depth phases, sPg, sPmP, and sPn.…”

Section: The Depth Of the Main Shockmentioning

confidence: 99%

Studies on the June 23, 2010 north Ottawa M W 5.2 earthquake and vicinity seismicity

Motazedian

2012

J Seismol

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“…Moderately sized events deeper than 5 km are able to generate Rayleigh waves, and the Rayleigh wave spectra also change with the focal depth (Aki and Richards 1980, Chapter 7). As other methods, such as the RDPM method (Ma 2010) or the teleseismic depth phase (sP and its reference phase, P) method (e.g., Goldstein and Dodge 1999) can be used to determine the focal depths for moderate earthquakes, it seems that there is no need to use the spectral ratio method for moderate earthquakes.…”

Section: Discussionmentioning

confidence: 99%

“…We have carefully studied the focal depths for the five largest events in the GHL earthquake swarm (Ma and Eaton 2009) using the RDPM method (e.g., Ma and Atkinson 2006;Ma 2010), as well as the amplitude information of the Rg wave. For comparison, we used the MPSR method to estimate the focal depth for the foreshock of the swarm.…”

Section: Error Caused By Epicentral Distancementioning

confidence: 99%

“…In Ma et al (2003), Ma and Atkinson (2006), Ma and Eaton (2007), Ma et al (2008), Ma and Eaton (2009), and Ma (2010), efforts were made at determining the focal depths for many small and moderate earthquakes in eastern Canada and vicinity by modeling regional depth phases (sPg, sPmP, or sPn: see Ma (2010) for definitions). However, many small earthquakes still do not have focal depth solutions.…”

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Depth determination of small shallow earthquakes in eastern Canada from maximum power Rg/Sg spectral ratio

Motazedian

2011

J Seismol

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For small earthquakes, focal depths can be estimated jointly when epicenters are located using the arrival times of Pg and Sg waves recorded at seismic stations close to the event. However, if regional network coverage is sparse, this approach does not give accurate results. An alternative solution is the use of the regional depth-phase modeling (RDPM) method when such depth phases are available. Small, shallow earthquakes can generate Rg waves, the amplitudes of which approximately attenuate exponentially with focal depth; whereas, the amplitudes of Sg waves are, on average, less dependent on focal depth. Based on these features, a method using the maximum power spectral ratio (MPSR) between the Rg and Sg segments was developed to determine focal depth. Tests show the focal depth solutions obtained by the MPSR and RDPM methods for five events in an earthquake swarm and one event acquired by inspection are in good agreement. The error in the MPSR-determined focal depth caused by the error in the epicentral distance is in the order of 0.1 km. The error in the focal depth when using a default focal mechanism is in the order of 0.5 km. The quality factor, Q does not generate a significant error. Using the average of focal depths can provide a more reliable solution. Using an azimuth of approximately 45°from the strike direction to generate the synthetic ratio curve can reduce the error. As with any other earthquake locating technique, a reasonable regional crustal model is required when the MPSR method is used. Case studies show that the MPSR method can be used to successfully determine focal depths for events as small as m N 1.6.

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An investigation of seismicity clustered near the Cordel Field, west central Alberta, and its relation to a nearby disposal well

Schultz¹,

Stern²,

2014

JGR Solid Earth

100

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Historically, seismicity documented in the Western Canada Sedimentary Basin has been relatively quiescent and earthquakes are usually restricted to the foreland belt of the Rocky Mountains. However, exceptional clusters of events, which have remained active for decades, are recognized in Alberta. In this study we investigate the seismicity in this region using data obtained from recently established regional arrays, emphasizing the relationship between a disposal well in the Cordel Field and a nearby cluster of previously reported earthquakes. We explore temporal correlations of wastewater pumping rates and local seismic activity dating back to 1960. We find that the first statistically significant increase in seismicity lags the onset of wastewater injection (October 1991) by~3.33 years. In particular, the waveform similarity of 32 events are analyzed from continuous data recorded at NOR, a nearby (~30 km) station operated by the University of Alberta starting in September of 2006. Results from this analysis suggest that many events are well correlated in the characteristics of the waveforms and thus are likely to share a similar origin and source mechanism. The most prolific of these multiplets repeats more than 10 times sporadically throughout the entire duration of recorded data from October 2006 to March 2012. Despite the limited availability of nearby stations, which adversely affects the resolution of our analysis, hypocenter depths could be relatively accurately determined from waveform synthesis and double difference methods. The results of our analysis provide first-order evidence that the seismicity is consistent with fluid injection-induced events.

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Focal Depth Determination for Moderate and Small Earthquakes by Modeling Regional Depth Phases sPg, sPmP, and sPn

Cited by 8 publications

References 8 publications

Studies on the June 23, 2010 north Ottawa M W 5.2 earthquake and vicinity seismicity

Studies on the June 23, 2010 north Ottawa M W 5.2 earthquake and vicinity seismicity

Depth determination of small shallow earthquakes in eastern Canada from maximum power Rg/Sg spectral ratio

An investigation of seismicity clustered near the Cordel Field, west central Alberta, and its relation to a nearby disposal well

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