microseismicity and tectonics in the granada basin (spain)hera.ugr.es/doi/15084498.pdf ·...

Microseismicity and tectonics in the Granada Basin (Spain)

D. Munoz a, A. Cisternas b,*, A. Udıas a, J. Mezcua c, C. Sanz de Galdeano d,J. Morales e, M. Sanchez-Venero c, H. Haessler b, J. Ibanez e, E. Buforn a,

G. Pascual c, L. Rivera b

aDepartamento de Geofısica, U. Complutense de Madrid, Madrid, SpainbInstitut de Physique du Globe de Strasbourg, Ecole et Observatoire de Sciences de la Terre, 5 rue Rene Descartes, 67084 Strasbourg, France

cInstituto Geografico Nacional, Madrid, SpaindDepartamento de Geologıa, Universidad de Granada, Granada, Spain

eInstituto Andaluz de Geofisica, Universidad de Granada, Granada, Spain

Received 15 August 2001; accepted 21 June 2002

Abstract

A microseismic experiment carried out in 1994 in the Granada Basin (Spain) permitted the precise recording of more than 80

local earthquakes. The dense distribution of the local network, with 40 to 50 instrumental records for each event, enabled us to

have well-controlled hypocenters, and also 10 reliable focal mechanisms. The above observations are interpreted together with

topographic data, neotectonics, and sub-surface information. Microtectonic observations in Sierra Elvira, Padul and Zafarraya

gave a set of fault planes and striae, which were interpreted in terms of the recent regional stress tensor. The actual stress tensor

obtained from the microseismic campaign data gives a regime in radial extension, with r1 vertical and r3 oriented NS to NNE.

Microtectonic information is coherent with these orientations, but closer to 3-axial extension. A set of 64 mechanisms obtained

from the permanent Andalusian network favors a NS orientation for r3. This results are interpreted in terms of the general

model implying the lateral ejection of the Betic ranges towards the Atlantic.

D 2002 Elsevier Science B.V. All rights reserved.

Keywords: Granada Basin; Andalucia; Microseismicity; Stress tensor; Neotectonics

1. Introduction

The Granada Basin is located within the Betic

Cordillera in southern Spain (Fig. 1). It constitutes,

together with the Guadix and the Baza basins, a

sequence of pull-apart basins along the Cadix–Ali-

cante right-lateral fault system (Sanz de Galdeano,

1983). This fault system, together with the Lorca–

Palomares–Carboneras left-lateral system and the

Gibraltar arc, limit a triangular wedge being expulsed

westwards by the NS convergence between Africa and

the Spanish stable block. The Betics are located along

the northern side of the wedge, the southern side

corresponding to the Moroccan Riff.

Several models (Platt and Vissers, 1989; Calvert et

al., 2000) have been proposed to explain the geo-

dynamics of the wedge, in particular the existence of

an internal zone, formed by the Alboran Sea, parts of

0040-1951/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.

PII: S0040 -1951 (02 )00338 -4

* Corresponding author. Fax: +33-390-24-0125.

E-mail address: [email protected] (A. Cisternas).

www.elsevier.com/locate/tecto

Tectonophysics 356 (2002) 233–252

Fig. 1. General geodynamics of southern Spain and northern Maroc (modified after Sans de Galdeano et al., 1995). The wedge limited by the Cadix–Alicante fault, the Gibraltar Arc

and the Lorca–Palomares–Carboneras system is expulsed westwards (large arrow). The Granada Basin may be recognized near the center.

D.Munozet

al./Tecto

nophysics

356(2002)233–252

234

the Betics and parts of the Riff, which has been

subjected first to compression and thickening, then to

the lost of the lithospheric mantle under the Alboran

Sea either by subduction or delamination, with the

corresponding thinning and extension (Blanco and

Spakman, 1993; Serrano et al., 1998). The surrounding

external zone is characterized by thrusting and folding

(Santanach et al., 1980; Sanz de Galdeano et al., 1990;

Calvert et al., 2000). Volcanism is calc-alkaline in the

Alboran Sea and internal zones, but changes to alka-

line-basaltic during the Quaternary in the external

zones.

Several neotectonic studies of the Granada Basin

has been carried out by Rodrıguez-Fernandez et al.

(1991) and by Sanz de Galdeano and Vera (1992) with

a very detailed description of its geodynamic evolu-

tion since upper Miocene, of its depositional sequen-

ces and active faulting.

Seismicity is moderate in this region and the best

information is that given by the Instituto Geografico

Nacional Seismic Data Files (IGN) and by the Cartuja

Observatory of the Instituto Andaluz de Geofisica

(IAG). Most of the earthquakes are within the crust,

but there are intermediate events (down to 150 km

depth) and a remarkable deep activity at a depth of

about 650 km (Buforn et al., 1995, 1997). Several

focal mechanisms have been computed for shallow

and intermediate earthquakes in the region (Carreno et

al., 1991a; Coca and Buforn, 1994; Bezzeghoud and

Buforn, 1999).

The purpose of this paper is to discuss the results of

a detailed microseismic survey carried out from May

21 to July 21 1994, with a dense local network within

the Granada Basin. Similar surveys had been per-

formed already in the same region in 1978 and in

1988 (Carreno et al., 1991a,b). The 1994 experiment

allows us to increase the information concerning

active faulting, and to obtain well constrained focal

mechanisms, which may be interpreted in terms of the

present regional stress regime acting on the basin.

This study gives a more detailed local stress field than

that of a more general survey carried out for the whole

of Spain (Herraiz et al., 2000). A comparison will be

made with the results obtained from records of the

permanent seismic networks installed in the region.

Microtectonic observations in Sierra Elvira, Padul and

Zafarraya, provide an independent data set, which

permits additional control.

2. Neotectonics

Overall reviews of the seismotectonics of the

Granada Basin may be found in Rodrıguez-Fernandez

et al. (1991), and in Morales et al. (1990). A more

local study of the Zafarraya basin, SW of the Granada

Basin, is found in Morales et al. (1991). The tectonics

and earthquake hazard of the Sierra Nevada, in

particular the one related to the Padul fault, has been

studied by Sanz de Galdeano (1996) and by Keller et

al. (1996).

The units belonging to the Internal zone are: (i) the

Nevado–Filabrides, formed by deposits of Paleozoic

and Triassic age which have been subjected to meta-

morphism. (ii) The Alpujarride, of Paleozoic to Trias-

sic age, also showing some degree of metamorphism.

(iii) The Malaguide deposits, of Mesozoic and Tertiary

age. On the other hand, marine deposits of Mesozoic to

Tertiary age not being affected by metamorphism

characterize the External zone.

The Granada Basin extends some 60 km along the

EW direction, and 40 km in the NS direction (Fig.

2a) and it is filled with Neogene sedimentary depos-

its. The height of the sedimentary basin decreases

from south (1000 m) to north (500 to 600 m)

(Morales et al., 1990, 1997). Maximum sediment

thickness on top of the basement is about 2.5 km

according to seismic sections (1.5 s reflection time

for the basement, Rodrıguez-Fernandez et al., 1991).

The basin is surrounded by topographic heights.

Thus, we find clockwise: (a) the Sierra Arana

(1943 m) towards the NE, along the contact between

the external and internal zones; (b) the Sierra Nevada

(3482 m) towards the SE, which belong to the

internal zone; (c) then the Almijara (2025 m), also

within the internal zone; (d) the Sierra de Tejeda of

the internal zone along the southern border; (e) the

Sierra Gorda (1671 m) at the SW, which belongs to

the external zone, and finally, (f) the Parapanda hills

(1604 m) at the northern border, well within the

external zone.

The most significant active fault systems (Fig. 2b)

observed on the borders of the Granada Basin are: (I)

The Cadiz–Alicante fault system, which is a right-

lateral fault oriented N60–70E, located on the north-

ern border of the basin. (II) The EW trending Alhama

de Granada–Alpujarra right-lateral wrench, showing

kilometric cumulated displacements, at the southern

D. Munoz et al. / Tectonophysics 356 (2002) 233–252 235

border of the basin. The 1884 Alhama de Granada

large destructive earthquake occurred along this fault.

(III) An impressive NW oriented normal fault system,

the Sierra Elvira–Padul–Durcal system, with 1.5 km

of cumulated vertical slip, is located along the eastern

side of basin. (IV) A set of NNE–SSW oriented,

normal and left-lateral faults affecting the internal

zone, but also some sediments, is present at the

eastern and SE side of the basin across Sierra

Nevada.

Fig. 2. (a) Topographic map of the Granada Basin. Elevation difference between contours is 100 m. For topographic heights around the Basin

see the text, Section 2. The topography reflects well the Cadiz–Alicante fault system next to the northeastern corner. The Alpujarra corridor

fault is also well defined by the sharp change in topography at the southern border of the basin. (b) Active tectonics of the Granada Basin with

the main fault systems (I to IV). The scale is the same as that of (a). C.Z.I.Z.E. is the limit between internal (southeast) an external zones

(northwest). The main sites described in the text are: Zafarraya (Z), Alhama de Granada (AG), Padul (P), Durcal (Du), Sierra Elvira (SE) and the

Cadiz–Alicante fault. The Alpujarra corridor fault of EWorientation is the large one at the bottom of the figure (Alp-C). The triangles show the

sites of microtectonic measurements.

D. Munoz et al. / Tectonophysics 356 (2002) 233–252236

Fig.2(continued).


3. Seismicity and the 1994 microseismic

experiment

The Granada Basin has a moderate permanent

activity with earthquakes of magnitude smaller than

5, nevertheless it has been the site of some large

earthquakes, or of seismic clusters. Historical earth-

quakes are shown in Fig. 3 according to their epicen-

tral intensity. They are spread all over the basin and

many affected the coastal region. The largest one

known is the big Alhama de Granada event of 1884,

which reached MKS intensity X (Udıas and Munoz,

1979). There is a concentration of historical activity

near Granada, though this may be an effect of the

density of population over there. Fig. 3 also shows the

instrumental seismicity previous to 1994, with mag-

nitudes larger than 4. Again the epicenters are spread

across the basin, and there is some concentration near

Granada. A large earthquake was registered in 1954

with epicenter at Padul and magnitude 7, but it was an

event at a depth of 645 km. A previous microseismic

experiment performed in 1978 (Carreno et al.,

1991a,b) registered events with magnitudes between

2 and 4. A seismicity cluster near Loja was the

dominant event during this experiment. A more

detailed microseismic campaign was carried on in

1988 with a dense network of 31 stations (Carreno

et al., 1991a,b), and it provided precise epicenters and

depths, though it lacked a reliable determination of

individual focal mechanisms.

Fig. 3. Historical seismicity and instrumental seismicity between 1900 and 1994. The 1884 Alhama de Granada earthquake had maximum

intensity X. The clustering of historical seismicity around Granada might be due to the large density of population over there. The largest

recorded event is the deep 1954 Padul earthquake (M=7.0, depth=657 km).


The 1994 campaign was designed to contribute

with another set of well-located events, which could

be correlated with tectonics, but also to obtain reli-

able individual focal mechanisms. About 49 stations

were distributed across the basin and its surround-

ings. Some were permanent stations of the Instituto

Andaluz de Geofisica (IAG), and of the Instituto

Geografico Nacional (IGN), and the rest were tem-

porary short period instruments (Fig. 4). Hypocen-

ters were determined through the HYPO 71 pro-

gram (Lee and Lahr, 1971), by using a three layered

crustal model over an homogeneous mantle (Layer

1: between 0 and 11 km with VP=6.1 km/s; Layer

2: between 11 and 24 km with VP=6.4 km/s; Layer

3: between 24 and 31 km with VP=6.9 km/s;

Mantle with VP=8.0 km/s). Only hypocenters with

Fig. 4. Station distribution during the 1994 campaign (May 21 to July 21). The triangles are the temporary stations, the inverted triangles belong

to the IGN National Network, and the crosses are the permanent stations of the Instituto Andaluz de Geofisica (IAG) network.


an rms <0.35 s were accepted. Fig. 5a shows the

location of 60 well located microearthquakes distrib-

uted all over the basin. A NS linear alignment of

activity is observed between Huetor-Tajar and

Alhama. The depths of most of the events are located

within the upper 15 km of the crust (Fig. 5b).

4. Focal mechanisms

One of the main purposes of this study was to

obtain instead of composite mechanisms, individual

focal mechanisms having in common the regional

stress regime (Rivera and Cisternas, 1990). In this

Fig. 5. (a) Epicentral distribution during the 1994 campaign and tectonic features. Two clusters may be observed, one going from Huetor-Tajar

to Alhama, and the other near Arenas del Rey. Duration magnitudes are between 0 and 4. (b) Depth distribution. Most of the events are

shallower than 15 km.


method, a set of individual mechanisms, together with

an average regional stress tensor compatible with

them, are determined so as to minimize a likelihood

function. Fig. 6 shows 10 individual mechanisms

obtained in this way in 1994. The selected events

had between 7 and 20 polarities each, and their

magnitude varied between 1.2 and 3.1. Most were in

normal faulting, but there were also some strike–slip

events. Appendix A and Table 1 show the nodal

planes and polarities corresponding to each mecha-

nism.

On the other hand, the IAG maintains a permanent

seismic network, and there is an accumulated set of

observations which, though less constraining for each

individual mechanism, have the advantage of being

more numerous due to the longer total time period of

the recordings. Thus, there is an additional set of 64

new focal mechanisms of local earthquakes (Fig. 7)

with magnitudes between 2.4 and 4.2, recorded

between 1988 and 1994. They were also obtained

from polarities of P arrivals by simultaneous inversion

of individual mechanisms and the regional stress

tensor (Rivera and Cisternas, 1990) (see Appendix

B and Table 2).

5. Microtectonic measurements

Microtectonic observations, namely the determi-

nation of active fault planes and striae in a region,

give complementary, and independent, information to

that obtained from focal mechanisms (Philip et al.,

1992). Single microtectonic measurements were per-

formed at Sierra Elvira (three sites), Padul (two sites)

and Zafarraya basin (six sites) during the 1994

campaign (Fig. 2b). Each microtectonic observation

consisted in measuring the azimuth and plunge of the

fault plane together with the rake of the correspond-

ing striae or slip vector, which gives the displace-

ment of the block on top of the fault plane (Fig. 8,

Table 3). The measurements are not necessarily made

on major faults, but on well defined, small scale,

features with various orientations. The variety and

quality of the fault mirrors and of the striations

Fig. 5 (continued).


permitted a reliable set of measurements. Moreover,

each site correspond to places of recent seismic

activity: Quaternary alluvial fans are cut by the fault

in Padul (Keller et al., 1996), the Zafarraya basin

was within the rupture zone of the large 1884,

Alhama de Granada earthquake and finally, the

Sierra Elvira fault is seismically active and, more-

over, shows perturbed Quaternary units (Santanach et

al., 1980). These observations are displayed in Fig. 8

with the same conventions used for focal mecha-

nisms, showing the fault plane, the auxiliary plane

and the slip vector. Most of the cases are normal

faults, but right-lateral or left-lateral strike–slips are

also present.

6. Regional stress tensor

From the above description of the main active

faults (Fig. 2b) we may obtain a qualitative idea about

the overall stress regime acting on the region: First,

since we have normal faults in different directions, we

may conclude that the stress regime is in extension

and that r1 is nearly vertical. Next, since the azimuth

of the Sierra Elvira fault is about NW, and its

character is purely normal without horizontal compo-

nent, we may assume that r2 is also oriented in a

direction close to NW, namely along the fault plane.

Finally, r3 should be oriented near a NE direction so

that the fault system IV (oriented NNE) might have a

Fig. 6. Focal mechanisms determined after the 1994 campaign (lower hemisphere equal area projection) and observed seismicity. Almost all of

the events are located within the basin.


left-lateral component, and that the Alhama de Gran-

ada fault and the Cadiz–Alicante fault system may

have a right-lateral component. We will show from

quantitative inversions of the stress tensor that this

picture is not unreasonable.

We made a comparison between (a) the stress

obtained from microtectonic measurements, (b) the

stress tensor calculated from local earthquakes

observed at 49 stations during the 1994 microseismic

experiment, and (c) from mechanisms obtained by the

permanent IAG network for the period 1986–1994

(Tables 1–3). We used a Monte Carlo method for the

three cases in order to have a common data processing

before comparison. We started with a randomly gen-

erated set of stress tensors and then selected the best 15

tensors which were compatible with both populations

of focal mechanisms, or with the set of microtectonic

Table 1

List of focal mechanisms (azimuth and dip of nodal planes) obtained

during the 1994 campaign

Focal mechanisms of the 1994 campaign

N First plan Second plan Sign

Azimj Dipj Azimj Dipj

1 339 33 162 57 +

2 198 79 290 80 +

3 86 46 192 75 +

4 357 18 194 72 +

5 276 10 112 80 +

6 343 32 149 58 +

7 58 8 165 88 �8 4 4 164 86 �9 195 85 92 21 +

10 113 54 341 47 +

The sign is positive for a normal fault and negative for a reverse

fault.

Fig. 7. Focal mechanisms (lower hemisphere, equal area projection) calculated from the polarities of 64 earthquakes recorded by the permanent

network of the IAG from 1988 to 1994.


data. The results of the inversion of the stress tensors

are given in Fig. 9. The conventions are those of

Rivera and Cisternas (1990). The principal stresses

are r1, r2, r3 in decreasing order. From these, we call

rz the one that is closer to the vertical direction, and ry,

rx (with ry>rx) are the ones closer to the horizontal

plane. The orientation of the stress deviator is given by

the Euler angles /, h and w, while the regional stress

regime (extension, compression or strike–slip) is

given by the shape factor R=(rz�rx)/(ry�rx).

Fig. 9a gives the Monte Carlo inversion from

microtectonic data (Table 3). In this case, the score

of 0.81 is good, the shape factor R=2.1, which

corresponds to 3-axial extension, r1 is nearly ver-

tical and r3 approaches the N05jW direction. The

fault planes and the striae are precisely known

before inversion, and they do not change in char-

acter during the calculations. Fig. 9b shows the

Monte Carlo stress inversion from the 10 individual

focal mechanisms obtained during the 1994 cam-

paign (Table 1). The fault planes are automatically

chosen from the two nodal planes in order to be

compatible with the resulting tensor. This inversion

produces a regime near radial extension (R=15.6 is

very large). In this case, r1 is practically vertical,

and r2 and r3 are horizontal but it is difficult to

differentiate them, as shown by the dispersion of

the best 15 solutions. The score of the inversion is

0.96, which is quite high. In this output, r1 is

vertical and r3 is oriented N25jE. The Monte

Carlo stress tensor inversion obtained from 64 focal

Table 2

List of the 64 focal mechanisms obtained from the data of the IAG

Focal mechanisms of the IAG network (1988–1994)

N Azimj Dipj Rakej

1 147.96 67.35 �28.62

2 11.99 17.40 �139.19

3 125.51 79.21 96.34

4 235.00 39.58 �31.22

5 21.16 49.51 �122.83

6 124.22 73.47 �22.55

7 124.98 73.75 �1.89

8 77.69 47.67 �150.89

9 34.00 52.76 164.22

10 130.35 83.20 75.73

11 81.59 22.68 �104.68

12 235.34 68.35 �109.94

13 131.88 14.30 �51.46

14 227.56 45.13 �36.49

15 29.16 38.52 �138.82

16 21.28 56.06 10.12

17 357.13 75.20 �10.75

18 240.02 17.56 81.38

19 95.15 53.82 �141.67

20 216.89 61.79 �51.99

21 137.61 48.27 �52.72

22 25.42 60.05 81.49

23 313.15 86.76 �87.20

24 227.17 47.42 �48.82

25 22.37 55.20 153.66

26 235.03 39.56 159.73

27 224.07 42.45 �8.59

28 320.14 86.28 �67.11

29 235.23 39.80 �132.85

30 214.54 62.18 �47.01

31 309.00 71.34 �105.15

32 237.80 58.66 �114.56

33 351.05 59.86 �61.10

34 120.67 71.83 �161.77

35 123.96 73.64 113.33

36 321.46 77.61 �80.18

37 82.28 40.61 �128.14

38 247.20 13.52 90.96

39 94.12 36.89 �107.33

40 123.93 73.92 112.14

41 333.75 82.48 �40.07

42 122.92 71.17 �93.68

43 18.06 13.87 �139.13

44 32.02 81.52 74.82

45 183.23 1.30 14.92

46 115.51 69.46 �163.97

47 233.53 39.23 21.68

48 232.70 39.72 6.90

49 33.04 41.65 �147.89

50 254.73 27.13 145.78

51 229.02 68.22 �95.87

52 49.61 34.72 �140.36

Focal mechanisms of the IAG network (1988–1994)

N Azimj Dipj Rakej

53 335.03 55.51 �88.40

54 21.51 67.58 47.71

55 117.62 76.74 138.13

56 93.66 39.99 �112.24

57 78.33 39.32 �130.07

58 322.65 68.37 �89.05

59 288.82 62.03 �123.43

60 229.26 41.26 �8.59

61 126.76 81.04 91.58

62 263.91 44.81 �143.44

63 230.88 75.75 �103.58

64 230.40 40.43 �1.47

Azimuth, dip and rake are given in degrees, the fault plane being

identified during the inversion.

Table 2 (continued)


Fig. 8. Fault planes and striae obtained by microtectonic measurements. The measurements are presented as focal mechanisms but the fault

plane is known without ambiguity. The arrows indicate the slip vector.


mechanisms (Table 2) is given in Fig. 9c. The focal

mechanisms were the result of applying the max-

imum likelihood inversion to the total set of polar-

ities from the data provided by the IAG. The data

set is larger than for Fig. 9b, but the number of

polarities per event is smaller. The result shows that

again r1 is near vertical. Nevertheless, it is even

more difficult to discriminate r2 from r3 since

R=51.4 is closer to radial extension. The smaller

stress r3 is oriented in a direction N10jW. The score

is 0.61, which is rather low, meaning that it is

difficult to fit all of the data.

7. Discussion and conclusions

The general tectonics of the Granada Basin is

characterized by a stress regime in extension, which

apparently differs from what might be expected

from the convergence between Africa and stable

Spain. Nevertheless, such a regime is compatible

with a pull-apart mechanism for the development of

the basin, and is consistent with the right-lateral

character of the Cadiz–Alicante fault system, and

the lateral ejection of the wedge limited by the

Cadiz–Alicante and Lorca–Palomares–Carboneras

fault systems.

Seismic activity in different periods shows a dis-

tributed character across the Granada Basin. Some

special events, like the 1985 Loja cluster (Carreno et

al., 1991b; Herraiz and Lazaro, 1991) or the 1884

Alhama de Granada earthquake (Munoz and Udias,

1981), are clearly related to active faulting.

The seismicity of the 1994 experiment is also

distributed over the basin, but there is one cluster

along a NS line from Huetor-Tajar to Alhama. Most of

the events are concentrated within the upper 15 km.

An overall qualitative picture may be obtained

from the main active faults, and other large geody-

namic elements. The pure normal faults oriented NW

at Sierra Elvira may be interpreted as an indication

that r2 is subparallel to the fault plane, and that the

motion is controlled by r1 and r3. The left-lateral

character of the fault system IV, oriented NNE, and

affecting the internal zones at the eastern border of the

Granada Basin, is compatible with a r3 direction

oriented NNE to NE. The right-lateral character of

the Alhama de Granada fault is also compatible with

such an orientation of r3.Microtectonic measurements at three key sites,

Sierra Elvira, Padul and Alhama de Granada, are

compatible with a 3-axial extension stress regime

having r3 oriented N05jW.

Ten well-determined individual focal mechanisms

obtained from the 1994 data set indicate a stress

regime close to radial extension, with r3 oriented

N25jE.A long-term seismic survey by the permanent

network of the IAG contributes with 64 individual

focal mechanisms, which are compatible with a stress

regime in radial extension. This data set is controlled

by a smaller number of stations than that of the 1994

experiment, but the large number of total polarities

used in the inversion compensates this.

A synthesis of the above results, based on three

independent data sets, and the larger active faults of

the region, confirms an overall extension stress pattern

in the Granada Basin with r1 vertical and r3 oriented

N25jE to N10jW.

Acknowledgements

This work received support from the Centre

Nationale de la Recherche Scientifique (CNRS,

France), the Instituto Geografico Nacional (IGN,

Spain), and the Instituto Andaluz de Geofisica

(IAG). We thank M. Bezzegoud for his careful

reading of the text and numerous suggestions.

Table 3

List of the microtectonic measurements (azimuth, dip, rake)

corresponding to the Sierra Elvira, Padul and Zafarraya regions

Neotectonic measurements

N Azimj Dipj Rakej

1 93.0 68.0 �130.0

2 45.0 75.0 �150.0

3 98.0 67.0 �101.0

4 87.0 84.0 �5.0

5 51.0 86.0 �167.0

6 103.0 90.0 �16.0

7 139.0 18.0 �83.0

8 110.0 90.0 �105.0

9 118.0 90.0 �50.0

10 155.0 45.0 �78.0

11 150.0 45.0 �83.0

The order corresponds to Fig. 8.


Fig. 9. Stress tensor inversions obtained from microtectonic measurements, the 1994 microseismicity experiment, and from 64 individual focal

mechanisms observed by the IAG. The orientation of the stress deviator, the shape factor R and the score are shown for each inversion. The best

15 solutions are shown in a lower hemisphere equal area projection. (a) Monte Carlo inversion from microtectonic measurements (neo2.out). (b)

Monte Carlo inversion of the 1994 individual mechanisms (mad.out). (c) The stress tensor obtained by Monte Carlo inversion from the 64 IAG

mechanisms obtained by maximum likelihood from polarities (iag0.out).


Appendix A

Individual focal mechanisms of 1994 and polarities. P and T axes are indicated. Black dots are compressions,

and white dots are dilatations. The polarities are used to determine the nodal planes, which are compatible with a

single stress regime.


Appendix B

Individual focal mechanisms for 64 local earthquakes obtained from data of the IAG, not including those of

Appendix A. Nodal planes and the one standard deviation ellipse error of the pole of the fault plane are given,

together with the slip direction. Black dots indicate compression and white dots dilatations.


References

Bezzeghoud, M., Buforn, E., 1999. Source Parameters of the 1992

Melilla (Spain, Mw=4.8), 1994 Alhoceima (Morocco,

Mw=5.8), and 1994 Mascara (Algeria, Mw=5.7) earthquakes

and seismotectonic implications. Bull. Seismol. Soc. Am. 89,

359–372.

Blanco, M.J., Spakman, W., 1993. The P-wave velocity structure of

the mantle below the Iberian Peninsula: evidence for a subducted

lithosphere below Southern Spain. Tectonophysics 221, 13–34.


Buforn, E., Sanz de Galdeano, C., Udıas, A., 1995. Seismotectonics

of the Ibero–Maghrebian region. Tectonophysics 248, 247–261.

Buforn, E., Coca, P., Udıas, A., Lasa, C., 1997. Source mechanism

of intermediate and deep earthquake in southern Spain. J. Seis-

mol. 1, 113–130.

Calvert, A., Sandvol, E., Seber, D., Barazangui, M., Roecker, S.,

Mourabit, T., Vidal, F., Alguacil, G., Jaborr, N., 2000. Geo-

dynamics of the lithosphere and the upper mantle beneath the

Alboran region of the western Mediterranean: constraints

from travel time tomography. J. Geophys. Res. 21 (B5),

10871–10898.

Carreno, E., Sanchez-Venero, M., Garcıa, C., Herraiz, M., Udıas,

A., Ibanez, J.M., Morales, J., Lopez-Casado, C., Sanz de Gal-

deano, C., 1991a. Microsismicidad de la region Granada–Ma-

laga, sur de Espana. Rev. Geofis. 47, 93–102.

Carreno, E., Galan, J., Sanchez Venero, M., 1991b. Microseismicity

studies in southern Spain. In: Mezcua, J., Udias, A. (Eds.),

Seismicity, Seismotectonics and Seismic Risk in the Ibero–

Maghrebian Region. Instituto Geografico Nacional, Madrid,

pp. 79–86.

Coca, P., Buforn, E., 1994. Mecanismos focales en el sur de Espana:

Periodo 1965–1985. Estud. Geol. 50, 33–45.

Herraiz, M., Lazaro, M., 1991. Microearthquake distribution in the

Granada Region. In: Mezcua, J., Udias, A. (Eds.), Seismicity,

Seismotectonics and Seismic Risk of the Ibero–Maghrebian

Region. IGN, Madrid, pp. 65–77.

Herraiz, M., De Vicente, G., Lindo-Naupari, R., Giner, J., Simon,

J.L., Gonzalez-Casado, J.M., Vadillo, O., Rodrıguez-Pascua,

M.A., Cicuendez, J.I., Casas, A., Cabanas, L., Rincon, P.,

Cortes, A.L., Ramırez, M., Lucini, M., 2000. The recent (upper

Miocene to Quaternary) and present tectonic stress distributions

in the Iberian Peninsula. Tectonics 19, 762–786.

Keller, E.A., Sanz de Galdeano, C., Chacon, J., 1996. Tectonic

geomorphology and earthquake hazard of Sierra Nevada, South-

ern Spain. 1a Conferencia Internacional Sierra Nevada. Inst.

Andaluz de Geof., Granada. 20–22 March 1996.

Lee, W.H.K., Lahr, J.C., 1971. HYPO71: A computer program for

determining hypocenter, magnitude and first motion pattern of

local earthquakes. USA Geological Survey, Menlo Park. Open

file report, pp. 75–311.

Morales, J., Vidal, F., De Miguel, F., Alguacil, G., Posadas, A.M.,

Ibanez, J., Guzman, A., Guirao, J.M., 1990. Basement structure

of the Granada Basin, Bethic Cordillera Southern Spain. Tecto-

nophysics 177, 337–348.

Morales, J., Vidal, F., Pena, J.A., Alguacil, G., Ibanez, J., 1991.

Microtremor study in the sediment-filled basin of Zafarraya,

Granada (Southern Spain). Bull. Seismol. Soc. Am. 81 (2),

687–693.

Morales, J., Serrano, J., Vidal, F., Torcal, R., 1997. The depth of the

earthquake activity in the Central Betics (Southern Spain). Geo-

phys. Res. Lett. 24, 3289–3292.

Munoz, D., Udias, A., 1981. Estudio de los parametros y serie de

replicas del terremoto de Andalucia del 25 de Diciembre de

1884 y la sismicidad de la region de Granada–Malaga. El Ter-

remoto de Andalucia de 25 de Diciembre de 1884. Instituto

Geografico Nacional, Madrid, pp. 95–139.

Philip, H., Rogozhin, E., Cisternas, A., Bousquet, J.C., Borisov, B.,

Karakhanian, A., 1992. The Armenian earthquake of 1988 De-

cember 7: faulting and folding, neotectonics and paleoseismic-

ity. Geophys. J. Int. 110, 141–158.

Platt, J.P., Vissers, R., 1989. Extensional collapse of thickened Con-

tinental Lithosphere: a working hypothesis for the Alboran Sea

and Gibraltar Arc. Geology 17, 540–547.

Rivera, L., Cisternas, A., 1990. Stress tensor and fault plane solu-

tions for a population of earthquakes. Bull. Seismol. Soc. Am.

80 (3), 600–614.

Rodrıguez-Fernandez, J., Sanz de Galdeano, C., Vera, J.A., 1991.

The Granada Basin. Doc. Trav. L’IGAL 14, 1–19.

Santanach, P.F., Sanz de Galdeano, C., Bousquet, J.C., 1980. Neo-

tectonica de las regiones mediterraneas de Espana (Cataluna y

Cordilleras Beticas). Bol. Geol. Min. XCI-II, 417–440.

Sanz de Galdeano, C., 1983. Los accidentes y fracturas principales

de las Cordilleras Beticas. Estud. Geol. 39, 157–165.

Sanz de Galdeano, C., 1996. Neotectonica y tectonica activa en el

sector de Padul–Durcal (Borde SW de Sierra Nevada, Espana).

1a Conferencia Internacional Sierra Nevada. Inst. Andaluz de

Geof., Granada. 20–22 March 1996.

Sanz de Galdeano, C., Vera, J.A., 1992. Stratigraphic record and

paleogeographical context of the Neogene basins in the Betic

Cordillera, Spain. Basin Res. 4, 21–36.

Sanz de Galdeano, C., Rodrıguez-Fernandez, J., Lopez-Garrido,

A.C., 1990. Les Cordilleres Betiques dans le cadre geodynami-

que neoalpin de la Mediterrannee occidentale. Riv. Ital. Paleon-

tol. Stratigr. 96 (2–3), 191–202.

Sans de Galdeano, C., Lopez Casado, C., Delgado, J., Peinado,

M.A., 1995. Shallow seismicity and active faults in the Betic

Cordillera. A preliminary approach to seismic sources associ-

ated with specific faults. Tectonophysics 248, 293–302.

Serrano, J., Morales, J., Zhao, D., Torcal, F., Vidal, F., 1998. P wave

tomographic images in the Central Betics–Alboran Sea (South-

ern Spain) using local earthquakes: contribution for a continen-

tal collision. Geophy. Res. Lett. 25, 4031–4034.

Udıas, A., Munoz, D., 1979. The Andalusian earthquake of 25

December 1884. Tectonophysics 53, 291–299.


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