Abstract

We investigate the crustal thickness and Moho topography underlying the Peninsular Ranges near the U.S.-Mexico border with an east-west array of 9 broadband stations spanning the Peninsular Ranges batholith to record P-to-S converted phases of teleseismic body waves. The converted phases are isolated by the teleseismic receiver function method. Signal enhancement is attained by a regularized time domain deconvolution technique that uses multiple events in the same source regions. Arrivals which we interpret as Ps (mantle P to crustal S converted phase) are identified at most of the stations. The differential travel times (Ps minus P) at sites west of a compositional boundary that separates the Peninsular Ranges Batholith into east and west zones indicate a relatively flat, deep Moho. Ps minus P times at sites east of the compositional boundary decrease eastward. 1D crustal velocity models under each site were constructed from 3D seismic tomography results and used to infer Moho depth from the Ps delays. The resultant Moho depth estimate varies laterally, with relatively constant 36 to 41 km thick crust in the western zone. In the eastern zone the crust thins rapidly from 35 km thick at the compositional boundary to 25 km at the edge of the Salton trough, a lateral distance of 30 km . The deepest portion of the Moho does not coincide with the topographic high, suggesting compensation via lateral density variations in the lower crust or upper mantle. We propose that the compositional boundary decouples the eastern and western portions of the batholith, and that the eastern portion has thinned in response to regional Miocene extension, or Salton trough rifting, or both.

Introduction

The Mesozoic Peninsular Ranges batholith is a major component of the southern California crust between the International border and the Transverse Ranges (Fig. 1). The batholith is adjacent to the actively rifting Salton trough [e.g. Lomnitz et al., 1970; Elders et al., 1972]. The batholith can be divided into western and eastern sections defined compositionally [Silver et al., 1979]: the western section is older and more mafic, and the eastern section is younger and more siliceous [Gastil, 1975; Silver et al., 1979]. The north-northwest striking boundary between the compositional domains is coincident with, or near, a step in the age, chemical, isotopic, geopotential, and seismic velocity trends across the batholith [Baird et al., 1974; Gastil, 1975; Oliver, 1980; Silver et al., 1979; Baird and Miesch, 1984; Gastil et al., 1986; Hearn and Clayton, 1986; Jachens et al., 1986; Gromet and Silver, 1987; Todd et al., 1988; Silver and Chappell, 1988; Silver, 1992; Ague and Brandon, 1992; Magistrale and Sanders, 1995]. These west to east compositional variations reflect differing source regions [e.g. Silver and Chappell, 1988]. The western batholith section formed in oceanic type lithosphere while the eastern section formed in continental lithosphere. The oceanic and continental lithosphere were juxtaposed during a late Paleozoic-Early Triassic event that truncated the western North America continental lithosphere [e.g. Burchfiel et al., 1992]. Thus, it is likely that the compositional boundary in the Peninsular Ranges represents the current surface expression of that major truncation event.

Summaries of estimates of crustal structure under the Peninsular Ranges are given in Howell et al. [1985]; Mooney and Weaver [1989]; Fuis and Mooney [1990]; and Frez and Gonzalez [1991]. The summary models typically show the Moho as planar and gently east dipping under the Peninsular Ranges at an uncertain depth. Inversions of earthquake P_g travel time data for three-dimensional velocity models recognized some lateral velocity variations across the Peninsular Ranges crust [Hearn and Clayton, 1986; Sung and Jackson, 1992; Zhao and Kanamori, 1992]. Magistrale and Sanders [1995] determined a detailed crustal P wave velocity model of the Peninsular Ranges from local earthquake arrival time inversions. The model images the compositional boundary as a 3 per cent velocity contrast (higher on the west) between 4 and 20 km depth. The velocity contrast corresponds to a density contrast between 4 and 20 km depth too small to produce the observed Bouguer gravity step at the compositional boundary [Oliver, 1980]. This suggests that a density contrast (corresponding to the compositional boundary) must persist the entire thickness of the crust, and that Moho topography, or density variations of the lower crust or upper mantle, or both, contribute to the gravity anomaly. This would be consistent with the entire thickness of the crust being involved in the late Paleozoic-Early Triassic truncation event, and also suggests relief on the Moho under the Peninsular Ranges [Magistrale and Sanders, 1995 ].

There was relative vertical motion between the east and west portions of the Peninsular Ranges batholith. Ague and Brandon [1992] used igneous barometry to define 7 km of synbatholithic dip separation (east-side up) between the eastern and western Peninsular Ranges batholith on a fault coincident with the compositional boundary. Todd et al. [1988] defined a shear zone containing highly strained rocks that extends for at least 40 km along the compositional boundary (south of about 33° 20´). Thomson and Girty [1994] examined kinematic indicators in the shear zone. They find an episode (118 to 115 Ma) of east over west reverse displacement followed by oblique-normal, east side down, movement from 105 to 94 Ma. The displacement episodes apparently reflect regional tectonic events: Cretaceous crustal thickening followed by Late Cretaceous extension, most likely due to gravitational collapse [Livaccar, 1991; Gastil et al., 1992; Thomson and Girty, 1994; George and Dokka, 1994]. Thomson and Girty [1994] suggest strain was concentrated in the mechanically weak join between oceanic and continental crust (that is, the compositional boundary). Magistrale and Sanders [1995] propose that Quaternary fault development has also been concentrated at this join. Thus, it is reasonable to investigate the influence of the compositional boundary on Peninsular Ranges crustal thickness in response to Tertiary tectonic events such as Miocene extension and extension associated with the opening of the Gulf of California and the Salton trough.

Here, we use the broadband teleseismic receiver function technique [Burdick and Langston, 1977; Langston, 1977, 1979; Owens et al., 1984; 1987; 1988; Ammon et al., 1990; 1993] to estimate crustal thickness across the Peninsular Ranges. The receiver function method isolates the direct P and the Ps (a mantle P wave converted to a crustal S wave at the Moho) phase arrivals of teleseismic earthquakes. The differential time between the P and Ps phases can be used to infer crustal thickness. This paper is a summary of the detailed analysis of Ichinose [1995].

Data and Analysis

We deployed a temporary nine-station broad band seismic array across the Peninsular Ranges batholith near the latitude of San Diego (Fig. 1). We identified records of 30 teleseismic events with impulsive P wave arrivals and high signal to noise for the receiver function analysis (Table 1). During processing, the P wave arrivals are identified visually and confirmed by reference to a Jefferys-Bullen travel time table; long period noise is eliminated with a 0.01 hz corner high pass filter; and the records are rotated into radial and transverse components.

We obtain the receiver functions using a regularized time domain deconvolution technique that used multiple events in the same source regions listed in Table 1 [Sipkin and Lerner-Lam, 1992; Gurrola et al., 1995]. Prominent converted phases can be identified at most of the recording stations within 5 s of the direct P phase. We construct 1D crustal velocity models under each recording site from the 3D crustal P wave velocity results of Magistrale and Sanders [1995]. That 3D model extends only to 20 km depth and so the crust below that depth is assigned the same velocity as the base of the 3D model. Moho depths are obtained from the Ps-P times by adjusting the thickness of the crust below 20 km depth to match the differential travel times. We assume that the crust is a Poisson solid (consistent with the Wadati analysis of Nava and Brune [1982]) to obtain S wave velocities from the P wave velocities.

Results and Discussion

Each station in the western portion of the Peninsular Ranges recorded a large amplitude converted phase 4.2 to 4.8 s after the direct P (Fig. 2). We identify that phase as Ps because it is the largest amplitude phase after the direct P. Depths to Moho are consistently 36 to 41 km (Fig. 3), indicating a relatively flat Moho. Station HONY had good recordings of events from all the source regions. At HONY, the Ps-P times are consistent for all backazimuths, and the relative delay of the PpPms and PpSms arrivals are in precise agreement with the Moho Ps-P delay (Fig. 4), providing additional evidence for a relatively simple, flat Moho beneath this part of the western Peninsular Ranges.

In the eastern portion of the Peninsular Ranges the time differential between the direct P and the largest converted phase steadily and dramatically decrease from 4.2 s at the compositional boundary to 3.1 s near the edge of the Salton trough (Fig. 2). The interface generating those converted phases appears to shallow by about 10 km vertical relief (from 35 to 25 km depth) over 30 km lateral distance, a dip of about 20° (this is an apparent dip because the strike of the seismometer array may not be normal to the interface strike). This interface is either the Moho or an intracrustal layer.

Parsons and McCarthy [1996], in a wide angle seismic refraction survey, defined a high velocity (6.9 km/s) lower crustal layer (>15 km depth) below and east of the Salton trough. This layer is spatially associated with relatively low upper mantle velocities (7.6 to 7.7 km/s versus 8.0 to 8.1 km/s beyond the area of the lower crustal layer). They attribute the layer to intrusions during both Miocene Basin and Range type extension and the younger Salton trough rifting. The western extent of the lower crustal layer was not determined. Also, a steeply dipping relatively dense lower crustal layer was inferred under the eastern Peninsular Ranges from gravity modeling by Fuis et al., [1982]. It is possible that the interface imaged by the receiver functions in the eastern Peninsular Ranges is the top of a lower crustal layer rather than the Moho. However, the easternmost station (MICA) has only a single prominent converted phase within 5 s of the direct P phase, suggesting that there is only a single high-impedance contrast, which we interpret as the Moho. The lower crustal layer imaged by Parsons and McCarthy [1996] has a characteristic seismic velocity signature, so our interpretation could be tested by finding the currently unknown eastern Peninsular Ranges lower crustal and upper mantle velocities.

Parsons and McCarthy [1996] determined a 21 km thick crust below the central Salton trough. Here, we estimate a 36 to 41 km thick crust below the western Peninsular Ranges. This implies that, even if the interface imaged by receiver functions is an intracrustal layer, the Moho below the eastern Peninsular Ranges must rise steeply to connect the western Peninsular Ranges and the Salton trough. The change in Moho depth may actually be accomplished by steps below our resolution to image here. We conclude that the Moho below the eastern Peninsular Ranges must shallow steeply to the east.

The identification of the Moho Ps phases is relatively unambiguous at some stations, especially in the western Peninsular Ranges (Fig. 2), but is less so at other stations. Assuming that our phase identification is correct, the main source of uncertainty in Moho depth derives from uncertainty in the average crustal P and S wave velocities beneath the stations. Our 1D velocity models are well constrained only above 20 km depth [Magistrale and Sanders, 1995], and we used the 20 km depth velocity values for depths between 20 km and the Moho. If we instead assume lower seismic velocities (the 14 km depth velocity values from Magistrale and Sanders, [1995]) for the crust below 20 km depth we obtain Moho depths that are 1.0-2.0 km shallower under the western Peninsular Ranges, and 0.3-1.0 km shallower under the eastern Peninsular Ranges. These uncertainties do not affect our conclusions.

Baker et al. [1996] analyzed receiver functions at PFO, a station in the eastern Peninsular Ranges north of our temporary array. They define a Moho dipping southwestward about 20°. Zhu and Kanamori [1994] used receiver functions to determine Moho depths of 30 km below PFO, and 38 km below BAR, a station in the western Peninsular Ranges just south of our temporary array (Fig. 1). These results are congruent with our observations. The lateral variations in crustal thickness identified here may explain the wide range of Moho depth estimates in earlier studies that analyzed earthquake and explosion body and surface waves assuming uniform layers (26 km [Thatcher and Brune, 1973], 31 km [Hadley and Kanamori, 1979], and 42 km [Nava and Brune, 1982]).

We hypothesize that the steep Moho slope under the eastern Peninsular Ranges batholith is due to the crustal thinning and rifting associated with the opening of the Gulf of California and the Salton trough. The large Moho relief under the eastern Peninsular Ranges batholith is unusual for the southwestern U.S. Other studies have demonstrated a surprisingly flat Moho under the Basin and Range province, even across regions that have extended by much different amounts [e.g. Hearn et al., 1991; McCarthy et al., 1991; McCarthy and Parsons, 1994; Parsons and McCarthy, 1996 ]. This consistent Moho depth is attributed to the incorporation into the ductile lower crust of various amounts of material derived from the upper mantle and mobilized by adiabatic melting during crustal extension [e.g. Gans, 1987]. This process apparently has not occurred below the eastern Peninsular Ranges.

The lack of correlation between Peninsular Ranges topography and Moho depths (Fig. 3) indicates compensation via lateral density variations in the lower crust or upper mantle rather than by Airy type roots. This is similar to the situation in the southern Sierra Nevada Mountains [Wernicke et al., 1996]. Lower crustal and upper mantle lateral variations can be produced by Salton trough rifting processes [ Fuis et al., 1982; Parsons and McCarthy, 1996].

These preliminary results indicate that the Moho has different attitudes below the eastern and western portions of the Peninsular Ranges: relatively flat in the west and relatively steeping dipping in the east. The change in Moho attitude occurs at the downdip projection of the batholith compositional boundary. The composition boundary has served as a locus of Mesozoic strain [Thomson and Girty, 1994] and may have in part controlled the location of Quaternary faults [Magistrale and Sanders, 1995 ]. These observations suggest that the composition boundary is a weak zone that penetrates the thickness of the crust and may decouple the western and eastern portions of the batholith. The compositional boundary appears to be the western boundary of crustal thinning associated with Miocene extension or Salton trough rifting, or both.

Acknowledgments: We thank the landowners and agencies for access to install the temporary seismometers; E. Baker for a copy of the deconvolution code and discussions; G. Girty for discussions; and the IRIS-PASSCAL program for the use of seismometers. Funded in part by a SDSU RSCA grant to S. Day.
 

Table 1.
 

Date-Time	Lattitude (°N)	Longitude (°E)	Mw	Depth (km)	Distance (°)	BAZ (°)
Columbia
5-31-94 17:41:58	7.35	-72.11	6.0	17	48.5	111.5
6-03-94 11:25:10	3.57	-78.84	5.8	11	45.9	121.3
6-06-94 20:47:43	2.95	-76.17	6.8	14	48.2	119.4
7-04-94 21:36:44*	15.00	-97.18	6.5	6	24.9	130.9
Argentina
4-29-94 07:11:29	-28.44	-62.78	6.8	572	79.6	133.6
5-10-94 06:36:27	-28.51	-62.87	6.9	599	79.6	133.7
8-19-94 10:02:53	26.52	-63.26	6.5	568	77.7	132.6
Vanuatu
4-18-94 17:29:54	-6.47	154.73	6.8	42	92.2	263.8
4-21-94 03:51:45	-5.68	153.95	6.6	44	92.5	264.9
7-13-94 02:35:59	-16.05	167.43	7.1	24	87.1	249.0
7-14-94 00:09:27	-16.05	167.17	6.1	22	87.3	249.1
7-22-94 16:57:54	-6.73	158.46	6.1	30	89.3	261.6
7-24-94 17:55:40	-17.31	167.68	6.6	13	87.7	247.8
7-29-94 07:53:31	-16.60	167.42	6.2	44	87.5	248.5
Kuril
7-21-94 18:36:32	42.31	133.16	7.2	476	81.5	315.2
8-14-94 00:46:22	45.53	150.24	6.0	21	69.8	310.7
8-18-94 04:42:59	44.60	150.21	6.4	22	69.7	310.5
8-20-94 04:38:50	44.80	148.75	6.2	36	70.6	311.2
8-28-94 18:37:22	44.88	150.07	6.6	9	69.7	310.8
8-31-94 09:07:26	43.70	145.99	6.2	70	72.9	311.2

Source parameters are from the fast USGS moment tensor solutions [Sipkin, 19xx].
* This event was used at station BWLW in place of the Columbia stack.
 

Figures and Figure Captions

Figure 1. The Peninsular Ranges in southern California. Shading indicates the approximate extent of the surface exposure of Peninsular Ranges batholithic rocks. Light lines are faults and the coastline. Dotted line is the compositional boundary, taken from Silver and Chappell [1988] and Baird and Miesch [1984]. Dashed rectangle shows the location of figure 3A. Triangles indicate the temporary seismic stations; squares are other stations mentioned in the text. Each temporary station consisted of a RefTek RT72A-07 24 bit recorder with a STS-2 seismometer. Data were recorded at 20 samples per second. Instruments were supplied by IRIS-PASSCAL from April to June 1994, and by Scripps Institution of Oceanography from June to September 1994. Abbreviation: SD, San Diego.

Figure 2. Receiver functions determined at each station (columns) for each source region (rows; see Table 1). The direct P arrivals are the peaks at zero time. The arrivals interpreted as Ps are indicated by crosses. The stations are displayed in west to east order; the Peninsular Ranges compositional boundary is between stations PINE and LGNA.

Figure 3. (A). Map of depth to Moho (see text for discussion of alternative interpretation for eastern stations). Depths (in km below sea level) are plotted at the conversion points (crosses) connected to the temporary seismic stations (triangles). Points A and B are the endpoints of the cross section shown in figure 3B. Dotted line is the compositional boundary. (B). Cross section of Moho depth (crosses; km below sea level), elevation (solid line; km above sea level), and stations (triangles). Note that the Moho depth does not correlate to the elevation. The compositional boundary is at km 50.

Figure 4. Receiver functions determined at station HONY in the western Peninsular Ranges. The lower four traces are the receiver functions found for each of the source regions (Table 1) and the top trace is a stack of the four lower traces. In the global stack, the PpPms and PpSms arrivals (which have opposite polarities) are evident at 14.5 and 19.0 seconds, respectively. Their relative delay is in agreement with the Moho Ps-P delay (4.5 s), indicating a relatively simple, flat Moho beneath the western Peninsular Ranges. The global stack was made without correcting for the ray parameter difference between Colombia and the other source regions (which have nearly identical ray parameters); this results in a difference of <0.1 s for the Colombia Ps arrival and <0.4 s for the Colombia PpPms arrival, significantly less than the half-width of the arrival peaks.

References

Ague, J. J., and M. T. Brandon, Tilt and northward offset of Cordilleran batholiths resolved using igneous barometry, Nature, 360, 146-149, 1992.

Ammon, C. J., G. E. Randall, and G. Zandt, On the non-uniqueness of receiver function inversions, J. Geophys. Res., 95, 15,303-15,318, 1990.

Ammon, C. J. and G. Zandt, Receiver structure beneath the southern Mojave Block, California, Bull. Seism. Soc. Am. , 83, 737-755, 1993.

Baird, A. K. and A. T. Miesch, Batholithic rocks of southern California- a model for the petrochemical nature of their source materials, U.S.G.S. Pro. Pap. 1284, 24 pp. 1984.

Baird, A. K., K. W. Baird, and E. E. Welday, Chemical trends across Cretaceous batholithic rocks of southern California, Geology, 2, 493-495, 1974.

Baker, G. E., J. B. Minster, G. Zandt, and H. Gurrola, Constraints on crustal structure and complex Moho topography beneath Pinon Flat, California, from teleseismic receiver functions, submitted to Bull. Seism. Soc. Am., 1996.

Burchfiel, B. C., D. S. Cowan, and G. A. Davis, Tectonic overview of the Cordilleran orogen in the western United States, in The Cordilleran orogen: conterminous U.S., The geology of north America volume G-3, edited by B. C. Burchfiel, P. W. Lipman, and M. L. Zoback, pp. 407-480, GSA, Boulder, Colo., 1992.

Burdick, L. J. and C. A. Langston, Modeling crustal structure through the use of converted phases in teleseismic body waveforms forms, Bull. Seism. Soc. Am., 67, 677-691, 1977

Elders, W. A., R. W. Rex, T. Meidav, P. T. Robinson, and S. Biehler, Crustal spreading in southern California, Science, 178, 15-24, 1972.

Frez, J., and J. J. Gonzalez, Crustal structure and seismotectonics of northern Baja California, in The Gulf and Peninsular province of the Californias, edited by J. P. Dauphin and B. R. T. Simoneit, pp. 261-284, AAPG Memoir 47, Tulsa, Okla., 1991.

Fuis, G. S. and W. D. Mooney, Lithospheric structure and tectonics from seismic-refraction and other data, in The San Andreas fault system, California, edited by R. E. Wallace, pp. 207-238, U.S.G.S. Pro. Pap. 1515, Washington, D. C., 1990.

Fuis, G. S., W. D. Mooney, J. H. Healey, G. A. McMechan, and W. J. Lutter, Crustal structure of the Imperial Valley region, in The Imperial Valley, California, earthquake of October 15, 1979, pp. 25-50, U.S.G.S. Pro. Pap. 1254, Washington, D.C., 1982.

Gans, P. B., An open-system, two-layer crustal stretching model for the eastern Great Basin, Tectonics, 6, 1-12, 1987.

Gastil, R. G., Plutonic zones of the Peninsular Ranges of southern California and northern Baja California, Geology, 3, 361-363, 1975.

Gastil, R. G., G. J. Morgan, and D. Krummenacher, Mesozoic history of Peninsular California and related areas east of the Gulf of California, in Mesozoic Paleogeography of the Western United States, edited by D. Howell and K. McDougall, pp. 107-115, Pacific section SEPM, Los Angeles, Calif., 1978.

Gastil, R. G., J. Diamond, and C. Knaack, The magnetite ilmenite line in peninsular California (abstract), Geol. Soc. Am. Abs. Prog., 18, 109, 1986.

Gastil, G., M. Wracher, G. Strand, L. L. Kear, D. Ely, D. Chapman, and C. Anderson, The tectonic history of the southwestern United States and Sonora, Mexico, during the past 100 m.y., Tectonics, 11, 990-997, 1992.

George, P. G. and R. K. Dokka, Major Late Cretaceous cooling events in the eastern Peninsular Ranges, California, and their implications for Cordilleran tectonics, Geol. Soc. Am. Bull., 106, 903-914, 1994.

Gromet, L. P. and L. T. Silver, REE variations across the Peninsular Ranges batholith: Implications for batholithic peterogenesis and crustal growth in magmatic arcs, J. Petrology, 28, 75-125, 1987.

Gurrola, H. G., G. E. Baker, and J. B. Minster, Simultaneous time domain deconvolution with application to receiver functions, Geophys. J. Intl., 120, 537-543, 1995.

Hadley, D. and H. Kanamori, Regional S wave structure for southern California from the analysis of teleseismic Rayleigh waves, Geophys. J. R. Astr. Soc., 58, 655-666, 1979.

Hearn, T. M. and R. W. Clayton, Lateral velocity variations in southern California. I. Results for the upper crust from P_g waves, Bull. Seism. Soc. Am., 76, 495-510, 1986.

Hearn, T. M., N. Beghoul, and M. Barazangi, Tomography of the western U. S. from regional arrival times, J. Geophys. Res., 89, 1843-1855, 1991.

Howell, D. G., J. D. Gibson, G. S. Fuis, J. H. Knapp, G. B. Haxel, B. R. Keller, L. T. Silver, and J. G. Vedder, C-3: Pacific abyssal plain to the Rio Grande rift: Geol. Soc. Am. Centennial Continent Ocean Transect 5, Boulder, Colo., 23 p., 1985.

Ichinose, G. A., Moho topography beneath the Peninsular Ranges, southern California from teleseismic receiver functions, B. S. thesis, 78 pp., San Diego State Univ., San Diego, 1995.

Jachens, R. C., R. W. Simpson, A. Griscom, and J. Marano, Plutonic belts in southern California defined by gravity and magnetic anomalies (abstract), Geol. Soc. Am. Abs. Prog., 18, 120, 1986.

Langston, C. A., Corvallis, Oregon, crustal and upper mantle receiver structure from teleseismic P and S waves, Bull. Seism. Soc. Am., 67, 713-724, 1977.

Langston, Charles A., Structure under Mount Rainier, Washington, inferred from teleseismic body waves, J. Geophys. Res., 84, 4749-4762, 1979.

Livaccar, R. G., Role of crustal thickening and extensional collapse in the tectonic evolution of the Sevier-Laramide orogeny, western United States, Geology, 19, 1104-1107, 1991.

Lomnitz, C., F. Mooser, C. Allen, J. Brune, and W. Thatcher, Seismicity and tectonics of the northern Gulf of California region, Mexico, Geofis. Int., 10, 37-48, 1970.

Magistrale, H. and C. Sanders, P wave image of the Peninsular Ranges batholith, southern California, Geophys. Res. Lett., 22, 2549-2552, 1995.

McCarthy, J., S. P. Larkin, G. S. Fuis, R. W. Simpson, and K. A. Howard, Anatomy of a metamorphic core complex: seismic refraction/wide-angle reflection profiling in southeastern California and western Arizona, J. Geophys. Res., 96, 12,259-12,291, 1991.

McCarthy, J. and T. Parsons, Insights into the kinematic Cenozoic evolution of the Basin and Range-Colorado Plateau transition from coincident seismic refraction and reflection data, Geo. Soc. Am. Bull., 106, 747-759, 1994.

Nava, F. A. and J. N. Brune, An earthquake-explosion reversed refraction line in the Peninsular Ranges of southern California and Baja California Norte, Bull. Seism. Soc. Am., 72, 1195-1206, 1982.

Oliver, H. W., Peninsular Ranges, in Interpretation of the gravity map of California and its continental margin , C.D.M.G. Bull. 205, edited by H. W. Oliver, pp. 17-19, Sacramento, Calif., 1980.

Owens, T. J., G. Zandt, and S. R. Taylor, Seismic evidence for an ancient rift beneath the Cumberland Plateau, Tennessee: A detailed analysis of broadband teleseismic P waveforms, J. Geophys. Res., 89, 7783-7795, 1984.

Owens, T. J., S. R. Taylor, and G. Zandt, Crustal structure at Regional Seismic Test Network stations determine from inversion of broadband teleseismic P waveforms, Bull. Seism. Soc. Am., 77, 631-662, 1987.

Owens, T. J., R. S. Crosson, and M. A. Hendrickson, Constraints on the subduction geometry beneath western Washington from broadband teleseismic waveform modeling, Bull. Seism. Soc. Am., 78, 1319-1336, 1988.

Parsons, T. and J. McCarthy, Crustal and upper mantle velocity structure of the Salton trough, southeast California, in press, J. Geophys. Res., 1996.

Silver, L. T., Tracking magmatic arc evolution across contrasting lithosphere settings in southwestern N. America, in The Second Hutton Symposium on the Origin of Granites and Related Rocks , edited by P. E. Brown and B. W. Chappell, Spec. Pap. Geol. Soc. Am., 272, 499, 1992.

Silver, L. T. and B. W. Chappell, The Peninsular Ranges batholith: an insight into the evolution of the Cordilleran batholiths of southwestern north America, Trans. R. Soc. Edinburgh Earth Sci., 79, 105-121, 1988.

Silver, L. T., H. P. Taylor, and B. W. Chappell, Some petrological, geochemical, and geochronological observations of the Peninsular Ranges batholith near the international border of the U.S.A. and Mexico, in Mesozoic crystalline rocks: Peninsular Ranges batholith and pegmatites and Point Sal ophiolite, edited by P. Abbott and V. Todd, pp.83-110, Department of Geological Sciences, San Diego State University, San Diego, Calif., 1979

Sung, L. and D. D. Jackson, Crustal and uppermost mantle structure under southern California, Bull. Seism. Soc. Am., 82, 934-961, 1992

Thatcher, W. and J. N. Brune, Surface waves and crustal structure in the Gulf of California region, Bull. Seism. Soc. Am., 63, 1689-1698, 1973.

Thomson, C. N. and G. H. Girty, Early Cretaceous intra-arc ductile strain in Triassic-Jurassic and Cretaceous continental margin arc rocks, Peninsular Ranges, California, Tectonics, 13 , 1108-1119, 1994.

Todd, V. R., B. G. Erskine, and D. M. Morton, Metamorphic and tectonic evolution of the northern Peninsular Ranges batholith, southern California, in Metamorphic and crustal evolution of the western United States, Rubey Volume VII, edited by W. G. Ernst, pp. 894-937, Prentice-Hall, Inc., Englewood Cliffs, NJ, 1988.

Wernicke, B., R. Clayton, M. Ducea, C. H. Jones, S. Park, S. Ruppert, J. Saleeby, J. K. Snow, L. Squires, M. Fliedner, G. Jiracek, R. Keller, S. Klemperer, J. Luetgert, P. Malin, K. Miller, W. Mooney, H. Oliver, R. Phinney, Origin of high mountains in the continents: the southern Sierra Nevada, Science, 271, 190-193, 1996.

Zhao, D. and H. Kanamori, P wave image of the crust and uppermost mantle in southern California, Geophys. Res. Lett., 19, 2329-2332, 1992.

Zhu, L. and H. Kanamori, Variation of crustal thicknesses in southern California from teleseismic receiver functions at TERRAscope stations (abstract), EOS Trans. AGU, 75, 484, 1994.