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Fay Odak Mekanizmaları. Deprem Odak Mekanizması Doğrultu Atımlı Fay Ters Fay Normal Fay.

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... konulu sunumlar: "Fay Odak Mekanizmaları. Deprem Odak Mekanizması Doğrultu Atımlı Fay Ters Fay Normal Fay."— Sunum transkripti:

1 Fay Odak Mekanizmaları

2 Deprem Odak Mekanizması

3 Doğrultu Atımlı Fay Ters Fay Normal Fay

4 Deprem Odak Mekanizması Sol atımlı Sağ atımlı Normal Fay Ters Fay Yüzeye çıkmamış Ters Fay

5 Deprem Odak Mekanizması

6 Fay Düzlemi Parametreleri Fay Düzlemi Kuzey Taban Bloku Deprem Odak Mekanizması Kayma açısı

7 Düşey Atım Deprem Odak Mekanizması Tam normal fay Tam ters fay Sol yönlü Tam Doğrultu atımlı fay Sağ yönlü Tam Doğrultu atımlı fay Dip= ? Rake=? Dip= ? Rake=?

8 Deprem Odak Mekanizması Yandan Görünüm Üstten Görünüm Yardımcı Düzlem Fay Düzlemi Yardımcı Düzlem Fay Düzlemi Projeksiyonu Yeryüzeyi Derinlik

9 Deprem Odak Mekanizması Doğrultu Atım Normal Faylanma Ters Faylanma Eğimli Ters Fay

10 Deprem Odak Mekanizması Fay Düzlemi Eğim Atımlı Fay (Normal) Eğim Atımlı Fay (Ters) Doğrultu Atımlı Fay (Sol yönlü) Genişleme Kısalma

11 Ters Fay veya Bindirme Fay Normal Fay Doğrultu Atımlı Fay Deprem Odak Mekanizması

12 Tam Normal Fay Normal Fay Bileşenli Doğrultu Atımlı Fay Tam doğrultu atımlı fay Düşey atım Ters Fay Bileşenli Doğrultu Atımlı Fay Tam Ters Fay

13 Deprem Odak Mekanizması

14 Fay uzunluğu ile Magnitüd arasında ki ilişki

15 Deprem Odak Mekanizması Deprem Süresi ile Magnitüd arasındaki ilişki

16 Deprem Odak Mekanizması Normal Fay Normal Fay Doğrultu Atımlı Fay (Sol yönlü) Doğrultu Atımlı Fay (Sağ yönlü) Okyanus sırtı boyunca oluşan depremlerin tektonizması

17 Deprem Odak Mekanizması

18 İlk hareket YUKARI İlk hareket AŞAĞI İlk hareket Belirsiz Deprem Odak Mekanizması

19 Üç farklı deprem için odak mekanizmaları ve bazı sismogramlar. Sıkışma bölgeleri siyah ile taranmıştır.

20 Çeşitli fay geometrileri için deprem odak mekanizmaları. Sıkışma bölgeleri siyah ile taranmıştır. Tam doğrultu atımlı mekanizma, ya NE-SW veya NW-SE yönlü düşey fay içindir. Eğim atımlı mekanizmalar ise N-S yönlü dört fay içindir. Doğrultu atımlı fay Eğim atımlı fay Ters fay Normal fay Düşey atımlı fay

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23 “Strike” ve “Dalım” açılarının ölçülmesi Bir fayın “Doğrultusu (Strike Açısı)” kuzey ile yaptığı açıdır. Dalım açısı (Dip angle) “Strike” açısının sağından ölçülür. Deprem Odak Mekanizması

24 “Rake” açısının ölçülmesi “u” fay düzlemi üzerinde ki kayma yönü Kayma (slip) yönü tavan bloğunun taban bloğu üzerinde ki göreceli hareketidir. “Rake”, rölativ olarak “strike” yönüne göre ölçülür. Taban Bloğu Tavan Bloğu

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26 Tam Doğrultu Atım Tam Düşey Atımlı Ters Fay Tam Düşey Atımlı Normal Fay Ters Fay Normal Fay Sol Yönlü Doğrultu Atımlı Fay Sağ Yönlü Doğrultu Atımlı Fay Sol Yönlü Eğim Atımlı Ters Fay Sağ Yönlü Eğim Atımlı Ters Fay Sağ Yönlü Eğim Atımlı Normal Fay Sol Yönlü Eğim Atımlı Normal Fay Fay Tipi

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31 1) Use the azimuth (205°) and the plunge (25°) of the dip vector (d) to plot the trace of the fault plane (f). The fault has a strike of 205° – 90° = 115°, and a dip of 25° (sameas the plunge of the dip vector). 2) Plot the pole of the fault plane (s’). 3) The reference strike is toward azimuth 115°. Given that the rake of the slip vector is +70°, it will not plot on a lower-hemisphere stereonet; however, the antipode of the slip vector (sva) does plot on the stereonet -- the antipode is 180° from the slip vector. The antipode is along the trace of the fault, 70° from the primitive circle as illustrated at left. Project a line from the slip vector antipode (sva) through the center of the plot (c) to just beyond the circumference of the stereo plot (i.e., beyond the primitive circle). That line, trending 47°, defines the trend of the slip vector. In the final presentation of the beachball diagram, we are going to leave a small portion of that line extending from the edge of the diagram to indicate the direction of hanging-wall slip. 4) Determine the plunge of the slip vector, which is identical in magnitude to the plunge of the slip vector antipode (sva): the slip vector plunges ~23° upward, with a trend of 47°. 5) Plot the trace of the auxiliary plane (ap) by using the slip vector antipode (sva) as the pole to that plane. Note that s’ is on the auxiliary plane. 6) The N axis (n) is located at the intersection of the fault plane and the auxiliary plane. Determine the trend and plunge of the N axis: it trends 133° and plunges ~8°. Örnek 1

32 7) Plot the trace of the plane whose pole is the N axis (dashed great circle). 8) Plot the P axis (p) 45° from s’ and 135° from the slip vector antipode (sva) along the dashed great circle. 9) Plot the T axis (t) 45° from s’ toward the slip vector antipode (sva) along the dashed great circle. 10) Determine the trend and plunge of the P axis (p): it trends ~37° and plunges ~21°. 11) Determine the trend and plunge of the T axis (t): it trends ~243° and plunges ~78°

33 12) Fill the quadrants through which the T axis passes with black, and the quadrants through which the P axis passes with white. Leave the short line indicating the direction of hanging-wall slip on the outside of the beachball diagram. 13) The map is a depiction of the corresponding fault as it exists near the focus of this earthquake. It is a reverse or reverse-oblique fault with a comonent of right-lateral slip. Örnek 2

34 1) Use the azimuth (115°) and the plunge (35°) of the dip vector (d) to plot the trace of the fault plane (f). The fault has a strike of 115° – 90° = 25°, and a dip of 35° (same as the plunge of the dip vector). 2) Plot the pole of the fault plane (s’). 3) Given that the azimuth of the slip vector is 50°, construct a line from the center of the plot (c) toward azimuth 50°, and locate the slip vector (sv) where that line intersects the trace of the fault (f). In the final presentation of the beachball diagram, we are going to leave a small portion of that line extending out from the circumference of the diagram to indicate the direction of hanging wall slip. 4) Determine the plunge of the slip vector (sv): it plunges ~27°. 5) Plot the trace of the auxiliary plane (ap) by using the slip vector (sv) as the pole to that plane. Note that s’ is located on the auxiliary plane. 6) The N axis (n) is located at the intersection of the fault plane and the auxiliary plane. Determine the trend and plunge of the N axis: it trends 150° and plunges ~30°.

35 7) Plot the trace of the plane whose pole is the N axis (dashed great circle). 8) Plot the P axis (p) 45° from s’ toward the slip vector along the dashed great circle (i.e., half way between s’ and sv). 9) Plot the T axis (t) 45° from s’ and 135° from the slip vector along the dashed great circle. 10) Determine the trend and plunge of the P axis (p): it trends ~12° and plunges ~52°. 11) Determine the trend and plunge of the T axis (t): it trends ~253° and plunges ~23°

36 12) Fill the quadrants through which the T axis passes with black, and the quadrants through which the P axis passes with white. Leave the short line indicating the direction of slip on the outside of the beachball diagram. 13) The map is a depiction of the corresponding fault as it exists near the focus of this earthquake. It is an oblique fault with components of normal and left-lateral slip.

37 Some problems 1. A published focal mechanism solution for a magntude (mb) 6.5 earthquake below northern Peru on October 28, 1997, lists the azimuth (trend) and plunge of the three principal axes as follows: T 247, 8; N 337, 0; P 69, 82. What is the strike and dip of the two nodal planes, one of which is parallel to the fault that generated the earthquake? What are the orientations (trend and plunge, or rake) of the two possible hanging-wall slip vectors? 2. In a published datafile listing the fault strike azimuth (right-hand rule), dip angle, and rake of hanging-wall slip vector, the data for a given earthquake are 135, 60, 120. Make a FMS beachball diagram (lower-hemisphere stereographic plot) for this earthquake. 3. In a published datafile listing the fault dip direction, dip angle, and rake of hanging- wall slip vector, the data for a given earthquake are 216, 65, Make a FMS beachball diagram (lower-hemisphere stereographic plot) for this earthquake. 4. A field geologist measures the orientation of a fault surface and the direction of hanging-wall slip indicated by grooves and striations on that surface. The fault’s strike- and-dip in the azimuth method is 35, 63SE, and the rake of the hanging-wall slip vector is 75° (as rake is defined by seismologists). For no particularly good reason other than a persistent case of seismologist envy, he wants to represent these data on his map as a pseudo-focal-mechanism solution beachball (which, by the way, is not a good idea). For the sake of humoring this poor sod, make a FMS beachball diagram from the field data. 5. You will be provided with a topographic map on which the surface trace of some faults are indicated. Two earthquake occur in the area. Given the location of the focus of each earthquake and their respective focal mechanism solutions, project likely fault planes to the surface to assess if any of the currently-mapped faults are active, or if there might be a previously unmapped fault in the area.

38 Deprem Odak Mekanizması Polarity of first P-wave arrival varies between seismic stations in different directions, depending on fault geometry. First motion is compression for stations located such that material near the fault moves ``toward'' the station, or dilatation, where motion is ``away from'' the station. When a P wave arrives at a seismometer from below, a vertical component seismogram records up or down first motion, corresponding to either compression or dilatation. Method requires understanding effect of earth structure on seismic waves

39 Shown are beachball representations of the P-wave radiation pattern for the three fundamental double-couple fault types: (a): pure strike-slip faulting, (b): pure dip-slip reverse (thrust) faulting, and (c): pure dip-slip normal faulting. Above each is a sketch of the fault geometry for that mode of faulting. (The auxiliary plane is shown as a dashed line.) The compressional quadrants are shaded, and the sign of the direction of vertical-component rst motion is included for each quadrant. (Usually these signs are not included.) Such plots are an ecient method to show trends in focal mechanisms for groups of earthquakes. See, for example, gures in the paper by Stein & Klosko, Such plots are also used to represent non double-couple mechanisms with nodal-plane projections replaced by nodal- surface projections. (After Gubbins, 1990, Figure 6.7.)

40 Pure dip-slip faults include normal faults and thrust faults. Only three of the four quadrants are observable in the beachball diagram for pure dip-slip faults, as shown at right. The center of the beachball plot is white for normalfaultmechanisms (a), and the center is black for reverse-fault mechanisms (b).Reverse-fault FMS diagrams look like my cat’s eyes. Oblique-slip faults have both strike-slip and dip-slip components. All four quadrants of a FMS beachball diagram are included for oblique slip earthquakes, as shown at left. If the center of the beachball plot is in a white quadrant (a), the fault has a normal component of slip, regardless of which of the two nodal planes is the fault; if the center is in a black quadrant (b), the fault has a reverse component of slip.

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42 Problem: Given a table of FMS data listing a fault with dip azimuth = 130°, dip angle = 60°, and rake of hanging-wall slip vector = –125°, reconstruct the corresponding focal mechanism solution “beachball” diagram and determine the approximate azimuth and plunge angle of the N, P and T axes. Describe the type of fault that produced the earthquake. Based on the focal mechanism solution, construct a map of what the fault might look like. Deprem Odak Mekanizması Some problems 1. A published focal mechanism solution for a magntude (mb) 6.5 earthquake below northern Peru on October 28, 1997, lists the azimuth (trend) and plunge of the three principal axes as follows: T 247, 8; N 337, 0; P 69, 82. What is the strike and dip of the two nodal planes, one of which is parallel to the fault that generated the earthquake? What are the orientations (trend and plunge, or rake) of the two possible hanging-wall slip vectors? 2. In a published datafile listing the fault strike azimuth (right-hand rule), dip angle, and rake of hanging-wall slip vector, the data for a given earthquake are 135, 60, 120. Make a FMS beachball diagram (lower-hemisphere stereographic plot) for this earthquake. 3. In a published datafile listing the fault dip direction, dip angle, and rake of hanging-wall slip vector, the data for a given earthquake are 216, 65, Make a FMS beachball diagram (lower-hemisphere stereographic plot) for this earthquake.

43 4. A field geologist measures the orientation of a fault surface and the direction of hanging-wall slip indicated by grooves and striations on that surface. The fault’s strike-and-dip in the azimuth method is 35, 63SE, and the rake of the hanging-wall slip vector is 75° (as rake is defined by seismologists). For no particularly good reason other than a persistent case of seismologist envy, he wants to represent these data on his map as a pseudo-focal-mechanism solution beachball (which, by the way, is not a good idea). For the sake of humoring this poor sod, make a FMS beachball diagram from the field data. 5. You will be provided with a topographic map on which the surface trace of some faults are indicated. Two earthquake occur in the area. Given the location of the focus of each earthquake and their respective focal mechanism solutions, project likely fault planes to the surface to assess if any of the currently-mapped faults are active, or if there might be a previously unmapped fault in the area.

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